Vista broke my website...

... so it appears. One of our websites at work doesn't appear to work with this new fangled Windows Vista. Lately we've been getting complains of the site not working properly, customers would log in, click through a page or two and then boom, back to the login page. From where I sit, the site is acting line the Session is being invalidated. It appears that everyone experiencing the problem is running Vista and IE7. I've tested it on IE6, IE7 and Firefox on XP and the site works just fine, so last variable appears to be Vista. At the moment, we do not have a Vista box (we've also been told not to install IE7 yet), but there is one on the way. Hopefully there's a setting somewhere in their new security "features" that will get the site working again.