You can create a new aspx file (maybe call it Popup) and in the calling form put some javascript. Sorry I only know how to do it with JS
<SCRIPT>
function fnOpenPopup(sPage,sArgs,sFeatures,bMode)
{
if (bMode == 'Modal')
window.showModelessDialog(sPage, sArgs, sFeatures);
else
window.open(sPage, sArgs, sFeatures);
}
</SCRIPT>
If you want to use this method I'll give you the parameters required.