Return a value to class from pageblocktable

Hi,

I have a pageblock table with some rows displayed. The user logged on picks one of the rows and I need the id which is a hidden column returned to my class.

This is what I have on the pageblocktable for this using the command link with a Param, what I get back is the id from the first row no matter which row I click on.

 <apex:column headerValue="Sel"> 
      <apex:commandLink action="{!assign}" value="Sel"> >  
        <apex:param name="tobeassignid" value="{!pitem.userdata.id}" assignTo="{!AssignID}" /> 
       </apex:commandLink> 
</apex:column>

Any help greatly appreciated. Thank you.