If you installed windows 2000 with xp all ready installed you will never get it to work properly.

Other than with windows Vista operating system (because it is a completely new system), any dual booting requires that the oldest operating system be installed first....there is no true way to get around this without the use of a third party boot manager that hides the MBR from each operating system installed.

Try to save what files you need saving and start over with installing the W2000 first then installing XP second.