Generally if you're getting BSOD's there is a driver or hardware issue, look in c:\windows\minidumps and email me the files, I might be able to tell you what's wrong (PM me for my email address).
OSX is a huge learning curve if you've never used it before, you'll spend some time on Google trying to find out how to do things you already know how to do on Windows.
How old is your desktop? Have you updated the drivers for it since you got it?