Dave - Premiere CS3 is available on the Mac
Also you could use
Parallels to run Windows on your Mac to use Windows software on your Mac (or you could just dual boot your Mac, so on boot up you get the option to boot into either OSX or Windows).
Also
CrossOver claims to work with Vegas, but it is not officially supported by them.
As an alternative to using Windows software on your Mac, you could look into
Final Cut Pro. I've heard nothing but good things about it.