Autodesk did not even test AutoCAD 2000 on Windows XP, so they won't support it in any way. However, the following may work.
1. Insert AutoCAD cd in the drive
2. Create a shortcut to the setup exe
3. Open the properties for the shortcut
4. Select the "compatibility" tab
5. Select run in compatibility mode and select windows 2000
6. OK the shortcut changes and run the shortcut
7. AutoCAD should install fine
8. Will it work flawlessly? Probably not.
Moreover, AutoCAD 2000 is a program designed for 32 bit computers, and XP has both 32 bit and 64 bit versions. I'd use the 32 bit version if I was forced to use XP. Personally speaking, however, I have a couple of dozen AutoCAD licenses, and made the decision to bypass Windows XP primarily because of the AutoCAD compatibility issues (among other considerations). If AutoCAD 2000 is your primary program, why would you even want to run it on XP. It's most stable on Windows 2000, and XP provides no additional benefits. If you need XP for other programs on the same computer, you may have better luck creating a dual boot configuration - XP on one, W2K on the other.
By the way, AutoCAD 2000 product retirement date is January 15, 2004, so don't expect to be able to use it for much longer.