firefox only has what, 5% marketshare against IE? IE7 shouldn't be too different from IE6, save some extra anti-spyware features and a boatload of security holes. Personally, I wouldn't touch the beta until it goes gold, and even then I'd wait a while =T
It has been a while since IE6 came out, but WinXP SP2 sorta revamped IE with the pop-up blocker and "increased privacy/security" features.