[SalesForce] Conditional rendering of a VF Page

<apex:pageBlockSection columns="1" id="Test" >
 <apex:inputcheckbox value="{!test.Same_Address__c}" label="Same as Above">//removed selected=true
    <apex:actionSupport event="onchange" rerender="Test" />
</apex:inputcheckbox>
  <apex:outputPanel rendered="{!NOT(test.Same_Address__c)}"> 
    <apex:inputField value="{!test.Contact_Surname__c}" />//Use labels as previous answer from Marcel says
    <apex:inputField value="{!test.Contact_First_Name__c}" />
    <apex:inputField value="{!test.Pos__c}" />
    <apex:inputField value="{!test.Addr__c}" />
 </apex:outputPanel>
</apex:pageBlockSection>


public with sharing class test{

    public Test__c test{get;set;}

        public Test(ApexPages.StandardController stdCtrl) {
        this.test=(Test__c)stdCtrl.getRecord();
        this.test=true;//observe the change in this line.Added this for proper behaviour on load 
       }

   }

Here is the working code and I have added comments where necessary to the code to help you. Just remove selected=true at first place.

A wrapper class is useful in this scenario. There is not enough controller code in the question to know for sure, but the implementation may look like something like this:

In the controller, define the wrapper class and change the method to return wrappers rather than sObjects. The controller will build the wrapper and set the isRendered member variable based on whether the sObject is contained in a Set someplace else in the controller.

public class ProposalWrapper {
    public Proposal__c proposal     { get; set; }
    public Boolean     isRendered   { get; set; }
}

public List<ProposalWrapper> getProposalWrappers() {
    List<ProposalWrapper> proposalWrappersToReturn = new List<ProposalWrapper>();

        // iterate over the list of Proposal__c sObjects
    for (Proposal__c proposal : ProposalsFromSomeList) {

        // create a wrapper to allow you to indicate visibility
        ProposalWrapper pWrapper = new ProposalWrapper();

        // stick the sObject into the wrapper
        pWrapper.proposal = proposal;

        // set the boolean field true/false based on whether the item is in the set
        pWrapper.isRendered = yourSet.contains(proposal);

        // add the wrapper to the list being returned
        proposalWrappersToReturn.add(pWrapper);
    }

    return proposalWrappersToReturn;

}

In the page:

<!-- iterate over the wrappers and use the boolean field to control visibility -->
<apex:repeat value="{!ProposalWrappers}" var="item">
    <apex:outputPanel rendered="{!item.isRendered}">
        <li>
            <apex:outputText value="{!item.proposal.Id}" />
            <apex:outputText value="{!item.proposal.Name}" />
    </apex:outputPanel>
</apex:repeat>