I have recently installed Fedora Core 3 on a external 160 gig hard drive. I didnt expect any changes to come to my computer when the external hard drive was not plugged in, but that was incorrect. The linux installation did not work, during boot it throws an attempted to kill init! error. I am more concerned with the fact that now my computer will not boot unless the external hard drive is in. Without it a "GRUB hard disk error" is thrown. I would like to get the default windows boot back, and getting linux to work would also be a plus. This is probably not enough info for anyone to give me a suggestion, but please get back to me with what you need to know to help me. Thanks.

Have a look at this thread for the post by harley51.

You'll need to re-install grub whilst in FC so it's on a Linux partition, rather than let it install to the MBR as you apparently did on the last install.
Then you can do as described and copy it over.

To resurrect your Windows system, boot from the XP CD, and select recovery centre, then do a FIXMBR - this will put the XP bootloader back, and you cann update boot.ini to include your linux system.