What you have to do, is when the computer is turning on, there is an option to access the "Bios" or "Setup" (usually delete, or F2/F10 sometimes F1...it should say), Find the option for "Boot Sequence/Order" and set it as follows:
1: CDrom
2: Floppy
3: HDD-0
Once that is done, pop the windows 2000 cd in the drive and save the bios settings (Option to SAVE AND EXIT), that will reboot your computer. It will then go through Regular POST tests, and then tell you "Hit any key to boot to disk" and then that gets you into the windows setup. The rest is self explanitory (Read the directions it gives you), and your on the road to reformatting. Good luck.