InfoPath Dev

I'm relatively new to InfoPath and desperately need some help.

I've put together a few forms already to replicate existing functionality from our Lotus Notes systems, but have hit a bit of a wall.

Basically I'm now trying to display a pop-up form or dialog from a button in the form.  This new form needs to be another InfoPath form.

Firstly, the doco seems to imply that you can only use HTML forms in the dialog...is that correct?

The doco also says to use the ShowModalDialog method of UI to display it, but this is where my big problem is.  I am using Visual Studio 2008 as the coding tool for InfoPath and for the life of me cannot access the XDocument class anywhere.  I have tried adding the Interop.InfoPath.SemiTrust reference in, but cannot find a way to instantiate any of the SemiTrust objects (like application, window, or xdocument) and tie them to my current document.
Can anyone point me in the right direction?

I've tried to get my head around tihs for hours and the documentation is only succeeding in confusing me further.

Thanks in advance.

 thisXDocument is a feature of the 2003 InfoPath object model and does not exist in the realm of the 2007 object model.  You're free to use the 2003 object model within InfoPath 2007, but you have to choose one or the other.

The 2007 object model is much friendlier to standard CLR features, and you're free to create your own WinForms, instantiate them, and display them, just as you would in any other Windows GUI application.