I found this in a MaximumPC magazine (issue January 2008). It is actually to downgrade to Windows XP but it should work for Windows 2000 Too.
I will give you the article and just try and see if it helps.
Downgrade to WinXP
1. Sadly you can't just pop in an XP disc while you're running Vista and hit install. Your first step is to determine whether you want to dual boot Vista or simply wipe Vista out and replace it with XP. If you're going to dual boot, use the DiscPart tool on the Vista installation disc (details here: http://tinyurl.com/fyzmf
) to create a second partition, or use a third-party tool such as GParted (http://gparted.sourceforge.net/
) to do the same thing. If your wiping out Vista, you can use the same tools to erase the Vista partition and start with a clean slate or just reformat while booting and installing from the XP setup disc.
2. If you're using a bleeding-edge PC, XP will likely choke when it comes time to start copying files, as it won't be able to see your hard drive. Why? XP can't handle AHCI mode on SATA drives, which most newer PCs have enabled. In your PC's BIOS, turn off AHCI mode (which should turn on ATA emulation) to make your installation easier. Or just load the drivers via floppy F6 drivers at boot. Alternately, you can slipstream AHCI drivers into a Windows XP installation disc, but this is a huge hassle.
3. With a blank partition ready and AHCI turned off, boot from an XP setup disc, preferably one with the newest Service Pack preloaded on it. Install the operating system normally. (If dual booting, Vista will remain on the C: drive; XP will show up on E: or another drive letter. The two OSes will be able to see each other, so be cautious when selecting the proper drive when installing apps.)
4. If you plan to dual boot, you'll need to repair the Master Boot Record, as XP overwrites the Vista-created MBR (Master Boot Record), which prevents Vista from loading. To fix it, boot from a Vista DVD and select "Repair your computer" on the Install Now screen. Select Startup Repair to finish the job.
5. Last Step: Set up dual booting. Any boot manager will do the job, or try the free (and Vista-friendly) EasyBCD (http://tinyurl.com/yousxx
). Boot into Vista (you won't have a choice), install and run EasyBCD, then click Add/Remove Entries. Change the drive to letter E: (or whatever drive letter you setup in Step 3), and then change Type to Windows NT/2k/XP/2k3. Click Add Entry, then Save. Reboot and the bootloader will now automatically appear.
As I said before, the same should work for Windows 2000. I was thinking about this while I was typing this up and I was going to say if you have a license for Windows XP the programs you have that run on Windows 2000 should work on Windows XP. If they don't work in Windows XP, I would recommend trying to run those programs in XP and Vista's (they both have this built in them) Compatibility mode which allows the operating system to run programs and tells the programs that it is the operating system you choose and not the one that you are trying to run it on.