If they're both on same partition you'll have to format and reinstall os. There's a few things you can do though:
If you want to save data you can use a partition manager to create another partition (if there's only 1) then install w2k and reclaim data.
You can boot from w2k disc and use repair console.
Or boot into safemode and show your boot.ini file details here which we can edit. (Use search for boot.ini then copy details into notepad.