Alright, so I'm trying to install debian on my machine. I have one ATA controller on my motherboard, which has a cd rom drive and a 120 gig hard drive with Windows XP NTFS Partition. I also have a PCI ATA controller which has another hard drive which is the one I am trying to install debian on. Well anyway I went through all the installation just fine and went through the partitioning steps when the installation said something about a windows XP partition on the other drive. It says that if that is my only other OS that it should be fine to put the GRUB boot loader on the master partition of my other drive. So I do what it tells me and then it asks me to pull out the installation media and reboot. When I reboot it says GRUB loading, and then it says Error 21. I looked this up just a second ago and it says it's an unknown boot problem. So I tried it again using Grub and in another spot on the other drive. still the same error. I even tried it with LILO on the master partition of the other drive again and it still says loading grub with the same error. I have no idea what to do from there.
in most cases, GRUB doesn't work properly if you install it in MBR/boot sector of other disk. unplug windows harddisk, plug-in Linux Harddisk as Primary Master. install GRUB in the MBR of harddisk.
Would I have to remove the grub boot loader from the other drive or something like that?
yes. if you have installed GRUB in MBR of Windows disk, try to boot up Windows. if it doesn't boot, you have to remove GRUB from there.
boot up from Windows Installation CD, select repair and execute fixmbr command. Windows will boot up on reboot.