popup window problem

[parames]

hi list..
i wanted to do something like this..

i have a form(in asp) where customer has to key in the userid.. the userid column is a dropdown list... there are more than 100 userid..
so, i want a popup window(in jscript) which show the name of the customer for each userid and also a combo box so that they can click the combo box and back to the parent (form) window .. how can i do this..
i know how to create a popup window but don't know how to create a combo box and let them do the selection back to parent window..
please help..

thanks alot

rgds,
parames.s