Just open up boot.ini in the C:\. Make sure you enable hidden files under Folder > Options. Open up boot.ini in notepad and you'll probably see the following lines:

multi(0)disk(0)rdisk(0)partition(1)\WINDOWS="Microsoft Windows XP Home Edition" /fastdetect

multi(0)disk(0)rdisk(0)partition(1)\WINDOWS="Microsoft Windows 98" /fastdetect

Just delete the one you don't want and save. Reboot and it should work.