What's everyone using to test in multiple IE versions? I have IE7 on my XP machine, and Multiple IE for IE6, but it's buggy (conditional comments don't work right).
Virtual machines. Microsoft gives free Virtual PC images with IE6, IE7 and IE8 beta for testing. They expire every few months but you can download new ones.
IETester is a newer tool that shows all IE rendering engines in tabs. It's not perfect either but conditional comments work in it. Good for quick checks, I still do final testing in a VM.