Until you hear any better, forthcoming IE 7.0 does not support Windows 2000. This could mean that many corporate users will open themselves up to various security issues, when they miss out on the security enhancements promised by this new browser.
The news that IE 7.0 will be available only to Windows XP SP2 (Service Pack 2) customers isn't likely to sit well with security experts who argue that the threat from the Firefox browser is at the center of Microsoft's aggressive anti-spyware and anti-virus plans.