Bewfore you do anything, make a backup of all important data, if you have ghost or true image, then make an image.
I think (doing this from memory) you will have to boot with the 2k drive in, then when in xp;
-boot.ini, they'll be a bout 5-6 lines, under [Operating Systems] remove the line that refers to windows 2000
You will prob be prompted to reboot.
This should now boot without reference to 2k, the reason your pc would not boot without the 2k drive in, was that the boot.ini was looking for that drive 1st and couldn't find it.
Hope this helps.