Hi,
Yes. You can do that. You will need to load your content into the dialog's ContentTemplate. The easiest way is to place a Panel inside the dialogs' ContentTemplate (right click the dialog, then select Edit Template -> ContentTemplate from the menu, then place a Panel control there). Once you have a Panel there, load whatever you would like to load into your Panel control and it no longer has anything to do with the dialog.
You can also find a set of basic dialog samples here:
http://demo.essentialobjects.com/Default.aspx?path=DialogYou would call the dialog's Show method to open the dialog on the server side. You do not need to explicitly hide it from code behind. Every time the page posts back the dialog is automatically closed.
Hope this helps.
Thanks!