Get a Mac, and run Windows dual-boot (free), or side by side with OS X, or simultaneously in the same screen.

If you're patient, you can have as many OS's running simultaneously as your RAM and HD allows. I have several different versions of XP (to test web development on IE 5.5, IE6, IE7) on the same Macbook.

Why limit yourself? Just be prepared to slowly but surely ditch Windows for OS X. It's happening to just about every software developer I work with, and this is from kids right out of college to folks with 10-15 years invested in Windows. I think my company's engineering staff are about 30% Mac and growing.