Sounds like you may have setup your bootloader on the MBR and screwed up your windows bootup.
You may need to use your Win installation CD, run a 'repair' and fix that bootup on the MBR. (Should have an option in the installation, I know my XP does.)
After that you would probably have to re-install the bootloader for Linux and NOT put that on the MBR. Put it on the first location. (I dont remember what it's called, I'm tired, but when I installed there were two options. MBR or the other. Put it on the other)
Anyway, I'm tired but I hope that helped a little...