In C553, variaudio crashes very frequently for me, with WinXP, which IS a supported OS for that app.
Variaudio in C6 (on WinXP) is a bit more stable, but I still get the odd runtime error.
Not as many as before, but they come occasionally. Now of course when there IS a crash, a reboot is required 
this too is not a WinXP-only thing, I believe it affects Win7 users too.
So thinkingcap, I am 99% certain this has nothing to do with OS, and everything to do with Steinberg code.
Also, I must point out that, as a C++ developer, there really is no excuse for allowing an application to terminate in this way, by throwing unhandled exceptions all the way to the top level like this… The app should catch all exceptions and handle them in a controlled fashion.
/FD