<apex:page controller="myleaddata" id="p1">	
  <apex:form id="f1">
<script src="https://ajax.googleapis.com/ajax/libs/jquery/1.11.3/jquery.min.js"></script>
      <script>
       $j = jQuery.noConflict();

      var a;
      function mydata()
      {
          a=document.getElementById('p1:f1:pb:my1').value;
          document.getElementById('p1:f1:pb:my2').value=a;
          
      if(a=='New Employee')
          {
alert('this is 1st alert');
              j$(document).ready(function() {
   j$('div#hidden').show();
});
      
         }
else
{
alert('this is 2nd alert');
              j$(document).ready(function() {
   j$('div#hidden').hide();
});
      
         }
 }
      
      
      </script>
 
       <apex:pageblock title="Basic lead info" id="pb">
           <apex:outputlabel value="company name" />
        <apex:inputtext value="{!companyname}" /><br/>
        <apex:outputlabel value="lead last name" />
        <apex:inputtext value="{!lastname}" /><br/>
          <apex:outputlabel value="phone number" />
        <apex:inputtext value="{!phone}" /><br/>
          <apex:outputlabel value="Email" />
        <apex:inputtext value="{!email}" /><br/>
          <apex:outputlabel value="Source" />
        <apex:inputtext value="{!source}" /><br/>
          <apex:outputlabel value="Referer" />
        
           <apex:inputfield value="{!le.Reffered__c}" id="my1" onchange="mydata()" /><br/>
           <apex:inputhidden id="my2" value="{!referer}" />
    
    </apex:pageblock>
      <div id="hidden" >
          
     
      <apex:pageblock title="address info"  >
      
          <apex:outputlabel value="street" />
          <apex:inputtext value="{!street1}" /><br/>
          <apex:outputlabel value="city" />
          <apex:inputtext value="{!city1}" /><br/>
          <apex:outputlabel value="state" />
          <apex:inputtext value="{!state1}" /><br/>
          <apex:outputlabel value="zip" />
          <apex:inputtext value="{!zip1}" /><br/>
          <apex:outputlabel value="country" />
          <apex:inputtext value="{!country1}" /><br/>
          
      
      </apex:pageblock></div>
      
      <apex:commandButton value="submit" action="{!myleaddata1}" />
           </apex:form>
    
</apex:page>

Apex:code

public class myleaddata {
    public string lastname{set;get;}
    public string companyname{set;get;}
    public string leadname{set;get;}
    public string phone{set;get;}
    public string email{set;get;}
    public string  source {set;get;}
    public string referer{set;get;}
    public string street1{set;get;}
    public string city1{set;get;}
    public string state1{set;get;}
    public string zip1{set;get;}
    public string country1{set;get;}
   
    
    public lead le{set;get;}
    
     
    public void myleaddata1()
    {
    if(referer == 'existing employee')
    {
      Opportunity opp=new Opportunity();
        opp.Name=lastname;
       opp.StageName='qualification';
        opp.LeadSource=source;
        opp.CloseDate=date.parse('8/10/2015');
        insert opp;
        
      }
      
      else
      {
       lead l1=new lead();
        l1.lastname=lastname;
        l1.Company=companyname;
        l1.Phone=phone;
        l1.email=Email;
        l1.LeadSource=source;
        l1.Reffered__c=referer;
        
        // address info part
       l1.PostalCode=zip1;
       l1.Street  =street1; 
       l1.City=city1;
        l1.state=state1;
        l1.PostalCode=zip1;
        l1.Country=country1;
        
        insert l1;
       }
    }
}