When you reinstall W2k it's best to reformat the partition first, not
doing so leaves files that the new install think is another OS.

To eliminate any other OS references from your boot-up:

1. Right click on MY Computer
2. Click on Properties
3. Click on Advanced
4. Click on Startup and Recovery
5. Under "Default OS", Pick the OS you want to boot.
6. Uncheck "Display list of operating systems"

Next time you reboot it will boot without intervention to the OS you
requested.

Hope this helps.