Windows 2000 support ended yesterday.
Ditto Windows XP SP2.
The latter is pretty easy; go to SP3. At least, it should be pretty easy, though Graham Cluley notes that that an alarming 77% of organisations are running Windows XP SP2 on 10% or more of their PCs.
As for Win2K, well, you should have known about it for some time and been planning for it!
Many large companies may have purchased an Extended Support Agreement with Microsoft that will provide them with critical security patches for XP SP2 even after today. The Extended Support Agreement doesn’t come cheap though.