Well, it won't be easy (if possible) to solve your problem.
You installed two antivirus at the same time into Windows 2k. Obviously, it will crash.
You need to get acess through DOS to registry files (BART CD from Alwil provides it, or boot into DOS and use NTFS for DOS application, then a registry editor for DOS).
Do you have any Registry backup (with ERUNT tool, for instance)?
Do you have an image of your system?
If not... maybe you'll have to consider reformat :'(