hmm, Good idea, But hard to do. Cz X Box has many many parts, which are different from Normal Computer and video configuration, so I think its way better to buy new,
Reason
1 - You may fail, If failed, Loose lot of money.
2 - Doesn't get the original quality, Graphics, and performance.
3 - And compatibility and copyright issues may occur.
I also do may experiments, Bt I want do things like this.. Its Too risky.
If you are willing to do I hope you may succeed. Good Luck.