I am still relatively new to developing VisualForce pages and customer controllers.  I would like to retrieve fields from a form and then pass the values to a webservice.  When I click on the actionFunction, the method is executed.  The form values are reset to blanks (at one time they stayed on the form).  I can see the debugtxt flash up on the screen before it is reset to blanks as well.  I would like for the form fieldss to not be blanked out, so I think this is a rerender issue.

VisualForce Page

<apex:page controller="Product_UsersController" sidebar="false" >
<apex:form >
<apex:pagemessages id="errors" />

    <apex:pageBlock title="Search" id="edit">   
    
    
    
    <table border="2" style="width:100%;">
    <tr>
    	<td style="font-weight:bold;width:200px;">
    		Find Product Users
    	</td>  
    	<td>
    		Filter Options: 
    		<input type="checkbox" name="chkShowRequesters" />Show Requesters
    		<input type="checkbox" name="chkShowAdministrators"/>Show Only Administrators
    	</td>
    </tr>
    </table>
    
    <table border="2" style="width:100%;">
    <tr>
    	<td style="width:200px;valign:top;border:1;">
    		<apex:pageBlock mode="edit" id="parameters">
    
    <script type="text/javascript">
    
    function getParameters() 
    {
    	try
    	{
    	
    	passVariables(
    		"SD",
    		"MD",
    		document.getElementById("txtFirstname").value,
    		document.getElementById("txtLastname").value,
    		document.getElementById("txtLoginname").value,
    		document.getElementById("txtEmail").value,
    		document.getElementById("txtCountry").value,
    		document.getElementById("txtCity").value,
    		document.getElementById("txtState").value,
    		document.getElementById("txtZip").value);
    	}
    	catch(err)
    	{
    		alert("getParameters Error: " + err.message);
    	}
    	
    }	  		
    </script>
    <apex:actionfunction name="passVariables" action="{!runSearch}" rerender="debug,errors">
    	<apex:param name="rbBusinessUnit" value=""  />
    	<apex:param name="slProduct" value="" />
    	<apex:param name="txtFirstname" value="" />
    	<apex:param name="txtLastname" value="" />
    	<apex:param name="txtLoginname" value="" />
    	<apex:param name="txtEmail" value="" />
    	<apex:param name="txtCountry" value="" />
    	<apex:param name="txtCity" value="" />
    	<apex:param name="txtState" value="" />
    	<apex:param name="txtZip" value="" />
    </apex:actionfunction>
    
    		<table border="2" cellpadding="2" cellspacing="2" width="200px">
    		<tr>
        		<td style="font-weight:bold;">Business<br />
            		<input type="radio" id="rbBusinessUnit" name="rbBusinessUnit" value="SD" checked="true" />SD 
            		<input type="radio" id="rbBusinessUnit" name="rbBusinessUnit" value="FD" />FD
        		</td>
    		</tr>
    		<tr>
        		<td style="font-weight:bold;">Product<br />
        	 		<apex:selectlist value="{!SDProducts}" id="slProduct"  size="1">
        	 			<apex:selectOptions value="{!SDProducts}" />
        	 		</apex:selectlist>
        		</td>
    		</tr>
    		<tr>
        		<td style="Font-weight:bold;">First Name<br />
        			<input type="text" id="txtFirstname" name="txtFirstname"  />
        		</td>
    		</tr>
    		<tr>
        		<td style="Font-weight:bold;">Last Name<br />
        			<input type="text" id="txtLastname" name="txtLastname"  />
        		</td>
    		</tr>
    		<tr>
    		    <td style="Font-weight:bold;">Login Name<br />
        			<input type="text" id="txtLoginname" name="txtLoginname"  />
        		</td>
    		</tr>
    		<tr>
        		<td style="Font-weight:bold;">Email<br />
        			<input type="text" id="txtEmail" name="txtEmail"  />
        		</td>
    		</tr>
    		<tr>
        		<td style="Font-weight:bold;">Country<br />
        			<input type="text" id="txtCountry" name="txtCountry"  />
       		 	</td>
    		</tr>
    		<tr>
        		<td style="Font-weight:bold;">City<br />
        			<input type="text" id="txtCity" name="txtCity" />
        		</td>
    		</tr>
    		<tr>
        		<td style="Font-weight:bold;">State<br />
        			<input type="text" id="txtState" name="txtState" />
        		</td>
    		</tr>
    		<tr>
        		<td style="Font-weight:bold;">Zip<br />
        			<input type="text" id="txtZip" name="txtZip" />
        		</td>
    		</tr>
    		<tr>
    			<td> 
    				
    				<button onclick="getParameters()">Search</button>
    				
    				<!-- <apex:commandButton value="Search" action="{!getParameters}" id="SearchButton" rerender="results,debug,errors" /> --> 
    			</td>
   			</tr>
    			  
    	</table>
    	</apex:pageBlock>  
    	</td>
    	</tr>
    </table>
    
     
    <apex:pageBlock title="Debug" id="debug">
      <apex:outputText value="{!debugtxt}" />           
    </apex:pageBlock>
    
	</apex:pageBlock>
</apex:form>    

</apex:page>

Custom Controller

public with sharing class Product_UsersController {
        
        
        public String debugtxt {get ;  set;    }
        public List<Product2> ProductTemp = new List<Product2>();
        public string selectedProduct {get; set;}
        
        public List<SelectOption> SDProducts 
        {
        	get 
        	{
        		ProductTemp = [Select p.SDProductID__c, p.Name From Product2 p 
        			where SDProductID__c > 'A' and Family like 'SD%'
        			order by p.Name];
        		SDProducts = new List<SelectOption>();
        		SDProducts.add(new SelectOption('','<== Optional Product ==>'));
        		for (Product2 temp : ProductTemp)
        		{
        			SDProducts.add(new SelectOption(temp.SDProductID__c, temp.Name));
        		}
        		return SDProducts;
        	  }
        	  set; }
        	  
//         public List<SelectOption> FDProducts 
//        {
//        	get 
//        	{
//        		ProductTemp = [Select p.SDProductID__c, p.Name From Product2 p 
//        			where SDProductID__c > 'A' and Family like 'FD%'
//        			order by p.Name];
//        		FDProducts = new List<SelectOption>();
//        		for (Product2 temp : ProductTemp)
//        		{
//        			FDProducts.add(new SelectOption(temp.SDProductID__c, temp.Name));
//        		}
//        		return FDProducts;
//        	  }
//        	  set; }
       
 
 		public Product_UsersController() {
 //			debugtxt = 'Complete search parameters and click run search to view selections';
 			system.debug('Entered Product_usersController');
 			
 		}
 		public  PageReference runSearch()  {
 			system.debug('***Entered runSearch function');
 			string rbBusinessUnit = apexpages.currentPage().getParameters().get('rbBusinessUnit');
 			string slProduct = apexpages.currentPage().getParameters().get('slProduct');
 			string txtFirstname = apexpages.currentPage().getParameters().get('txtFirstname');
 			string txtLastname = apexpages.currentPage().getParameters().get('txtLastname');
 			string txtLoginname = apexpages.currentPage().getParameters().get('txtLoginname');
 			string txtEmail = apexpages.currentPage().getParameters().get('txtEmail');
 			string txtCountry = apexpages.currentPage().getParameters().get('txtCountry');
 			string txtCity = apexpages.currentPage().getParameters().get('txtCity');
 			string txtState = apexpages.currentPage().getParameters().get('txtState');
 			string txtZip = apexpages.currentPage().getParameters().get('txtZip');
 			
 			
 			debugtxt = 'Business Unit: ' + rbBusinessUnit;
 			debugtxt = debugtxt + '; Product: ' + slProduct;
 			debugtxt = debugtxt + '; First Name: ' + txtFirstname;
 			debugtxt = debugtxt + '; Last Name: ' + txtLastname;
 			debugtxt = debugtxt + '; Login Name: ' + txtLoginname;
 			debugtxt = debugtxt + '; Email: ' + txtEmail;
 			debugtxt = debugtxt + '; Country: ' + txtCountry;
 			debugtxt = debugtxt + '; City: ' + txtCity;
 			debugtxt = debugtxt + '; State: ' + txtState;
 			debugtxt = debugtxt + '; Zip: ' + txtZip;
			system.debug('*** ' + debugtxt);
 			return null;
 		}
}