I have a XP Virtual PC with .NET 3.5 and .NET 4.0 installed (no development environment ... i.e. Visual Studio 2008 or 2010) and I created a simple WPF 4.0 application and tried to Snoop it.
Snoop can see the application, but for some reason the ManagedInjectorLauncher32-4.0.exe crashes. So, it seems as if I'm having problems on XP too.
Another thing to note, though, is that it isn't crashing silently ... like yours is.
I'm going to see if I can get a development environment going in a separate Virtual PC and see if I have still have this problem.
I still recommend trying to debug it yourself too. Good luck. And again, let me know if you find anything out.