When you are into your bios one of the options you can scroll down to should be "Automattically configure for optimum settings" or something similar.

Did you have linux on it in your xbox?
I ask this because xbox were shipped with 8GB HDD went up to 10GB after a while.
If so, it maybe because it still has xbox software and linux on it that you are getting problems.

I have read that xbox HDD are password protected and that you can't do anything with them unless you have the password. They need this password to run in the xbox, so that could be a problem also.

Other than that I'm all out of ideas, sorry.

EDIT: Did you have your Xbox chipped? I'm asking because I want to make mine xbox a media centre with my old 200GB HDD, but if I need to buy a chip and all that I might not bother...