Prior to the release of SP2 for Windows XP, I would have said there wasn't
much to be gained from upgrading if you've already purchased Windows 2000.
The security features of Windows XP SP2 are the primary reasons for
upgrading. If you have laptops, definitely get XP SP2 on those systems.
Windows Firewall, when controlled with group policy, is a good way to ensure
that you don't get the latest network worm brought straight into your
network.
Internet Explorer is significantly enhanced in XP SP2 and for most systems,
it boots a lot more quickly than Windows 2000. Added to that, there are no
more service packs planned for Windows 2000 and although there's life left
in Windows 2000, it's probably time to at least consider when you will
upgrade.
On the other hand, many companies acquire the latest OS when they upgrade
their systems. If you have systems with, let's say, 6 months to a year of
life, a Windows XP upgrade is expensive when you will be getting XP with
their replacements. If Windows 2000 is working well, then it's often
difficult to justify upgrading. If things are not going so well and you're
doing the work in ripping out the infrastructure and replacing it, it makes
sense to get the latest OS at the same time.
Oli