Hi, do you have any more details on the project?
If this is a 2D game, it should be very straightforward to port, as Microsoft has put mechanisms in place to make that easy. 3D is also doable in most cases.
There are also other things that can pose difficulty, such as if you are using networking in your game, or XACT for audio.
Nevertheless, I have been working with XNA since version 1.0, and am quite confident we can get this game working in Silverlight. I hope to hear from you soon.
Thanks,
-Brian Schwind