your xbox hd problem
The problem is that the xbox hd uses a filesystem called FATX which cannot be read by a normal windows pc. There are ways to install windows on your xbox, all of which require a modded xbox. You can do a softmod on your xbox. When it is installed you will be able to do anything you can do with a modchip. I have written serveral tutorials on how to install windows on your xbox, but i would suggest you use linux. Its easy to install and easy to use.
If you install windows it will be a lot slower than linux, because it uses an emulator. It is legal to install windows and linux on your xbox. The answer to your other question is that you cannot install windows xp on your xbox no-matter what emulator you use. The best version of windows which you can install on your xbox is 2000, which will give you a speed of around 600mhz.
So don't even try running anything like Star Wars : Battlefront ;-)
Troy,