The XBox is a Pentium III 733 mHz with 64 megs of RAM. Now, I have an ancient notebook that's a Pentium III 900 mHz with 64 megs of RAM. Windows 2000 is slow as shit on it. Guess how Windows 2000 will run on the XBox?
Now, have you ever tried to play a 3D game without a video card?
Because, with Windows on the XBox, there are no device drivers for the onboard GPU. So you're basically operating without a video card.
Put those things together.
The BIOS isn't the problem. <