Is there a way to convert an XNA project to a Silverlight project? I've never actually used Silverlight, but I like the prospect of transitioning my XNA project for use on the web.
Of course, I would prefer to make as few changes to the original code as possible.
Check out the SilverSpirte project.
Your mileage may vary.
http://silversprite.codeplex.com/
I was able to get a very simple 2d-based game running on SilverLight 3.
Silverlight doesn't support the XNA rendering API. You'll most likely need to rework your entire graphics pipeline to go away from XNA and into Silverlight's drawing API, which is quite different.
If you are still in the process of developing your XNA project, and you plan to port it, you would be doing a diservice to yourself if you didn't ensure that you architected your project in a manner that structures your program flow into tiers.
Keep your presentation/display tier seperate from the tier that is responsibile for your heavy lifting and logic, and in doing so, porting your project to another .NET technology interface will be as simple as creating a new presentation layer and plugging it into your logic layer.
Might be worth checking out Balder. A bit on the side perhaps, Balder will not convert your XNA project, but is rather a 2D/3D graphics engine that runs on both Silverlight and XNA.