I would like to create a custom visualforce page for creating a new task. Scenario: user clicks a button on the Activities related list on the parent object. That button launches a VF force page with both standard fields and custom fields for the Task. User populates those fields, then clicks Save. 

I've tried all sorts of things hobbled together from research online, but so far, no luck. 

(I'm a newbie at VF and apex)

Here's my current VF Page code:

<apex:page standardController="Task" extensions="extension_task">
<apex:form >
<apex:pageBlock mode="edit">
<apex:pageblockButtons >
<apex:commandButton value="Save" action="{!save}" />
</apex:pageblockButtons>
        <apex:pageBlockSection title="Quick Edits" columns="1">
            <apex:inputField value="{!Task.Whatid}"/>
            <apex:inputField value="{!Task.Subject}"/>
            <apex:inputField value="{!Task.Representative__c}"/>
            <apex:inputField value="{!Task.Category__c}"/>
            <apex:inputField value="{!Task.Comments__c}" style="width:400px; height:200px"/>
            <apex:inputField value="{!Task.Perceived_Call_Value__c}"/>
            <apex:inputField value="{!Task.Referred_To__c}"/>
            <apex:inputField value="{!Task.Interaction__c}"/>
        </apex:pageBlockSection>
    </apex:pageBlock>
</apex:form>

</apex:page>


Here's the apex class extension:

public class extension_task{

    Task task = new Task();
   
    public extension_task(ApexPages.StandardController controller) {
      this.task = (Task)controller.getRecord();  
    }

}

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I think a problem is that Task cannot be used as a StandardController. I tried setting the StandardController="ACA_Member__c", but that gives me an error (Error: Unknown property 'ACA_Member__cStandardController.Task'). It seems I should be able to use my custom object with standardController based on this page (http://www.salesforce.com/us/developer/docs/pages/Content/pages_controller_std_associate.htm).

Thanks any advance for any help!