I was installing the GRUB loader and I accidentally installed it on my Windows partition while following the tutorials. (setup (hd0,0)...evidently, that was my windows partition) My files on the Windows are still there, but when I try to boot from the Windows partition, it wouldn't. Then I even "fdisk /mbr" and when I booted it, it said "Missing Operating System." Is there any way I can somehow repair my windows partition? Or possibly undo these changes? Thanks in advance.

If it's Windows2000/XP, then just copy ntloader (or what it is called) along with a boot.ini to the root. Of course, if it's NTFS that'll get really hard.

If it's Windows~~ then it's some other file :/

where will i find the ntloader and boot.ini? and how exactly do i go about putting that in the root or something?

SYMPTOMS
When you try to start your Microsoft Windows 2000 Server-based computer, you receive the following error message:

Missing Operating System
The startup process does not continue.
CAUSE
The incorrect partition is marked active.
RESOLUTION
To resolve this issue, you must change your computer's active partition. Fdisk.exe is a tool with which you can modify the active partition. You can run Fdisk.exe from a bootable 3.5-inch disk that was created in Microsoft Windows 98.

Make sure that both the linux and Windows partitions are set active. And you do want grub to be on your root partition, you just have to add Windows to your bootloader script. In order to restore your partition, boot into the Windows CD and choose recovery console and there's something there to fix the mbr. Then install grub, and make sure that you have the extra lines to give an option to boot into Windows.