Basically for isolation purposes you cannot talk directly to objects inside the .ascx

Look at:
http://www.learnasp.com/students/charlescarroll/sourcecode-searcheruc.aspx
and see the way that we grab the selected item  from the listbox

public choice as string

Sub Page_Load(S As Object, E As EventArgs) 
    If ispostback=false THEN
        ....
    ELSE
        choice=thelist.selecteditem.text
    END IF
End Sub