Ciao Gianluca,
there should be a special class that permit to include a VO GUI window in a WinForms application, and also another class for the way around: to use WinForms windows in a VO GUI application.
Please look at the first two samples in this page:
http://www.govulcan.net/portal/Examples/MoreSamples/tabid/105/Default.aspx
I have tried (with Chris's help) another thing: include a WinForms control in a VO GUI windows (xported to X# of course), and this works like a charm.
Wolfgang