Hi

for hiding button in order related list at particular stage in proposal,follow the following code. create a page and override the view page of particular object

CODE

<apex:page standardController="Opportunity">

    <script src="/js/functions.js" type="text/javascript"></script>
    <script type="text/javascript" src="/soap/ajax/16.0/connection.js"></script>    
    <script type="text/javascript" src="/soap/ajax/16.0/ajax.js"></script>   
    <script type="text/javascript">

    window.onload = init;

    function init()
    {
              
     
     if('{!Opportunity.StageName}'== 'New Opportunity'||'{!Opportunity.StageName}'== 'Broadband Ordered')

****** the above if condition is to to which opportunity stages the button should hide in releted list************

     hideConvertButton2("newButton");

     }
         
     
     
     
    function  hideConvertButton2(btnName){
    try{

                  var convertButton3 = document.getElementsByName("new00NO0000000OYOD");

******the above ID(new00NO0000000OYOD) is the id of the button to which we should hide*********************

                  convertButton3[0].className="btnDisabled";

                  convertButton3[0].disabled=true;

                  convertButton3[1].className="btnDisabled";

                  convertButton3[1].disabled=true;
                }

        catch(e) {

            //var ee = e.message || 0; alert('Error: \n\n'+e+'\n'+ee);

        }

    }
           
             
       
    </script>

      <apex:form >        

        <apex:Detail subject="{!Opportunity.ID}"  relatedList="true" >            

********instead od opportunity.id you should give proposalobject.id*********************************

        </apex:Detail>                   
        
        

     </apex:form>


</apex:page>