Easy Solution .... run Program Compatibility Wizard, found in the WinXP start menu. Choose Win 2000 mode. Select "setup.exe" on CAD CD and you should have no problems.
Sorry people, don't know what all the smoke is about, I am using Acad 2000 in a XP OS without any problem. Installed Acad as though it was made for XP and presto no problem.
Much to the contrary of others I am also using Norton 2003.