Mootilda is right, the 360 out of the box is not able to have windows installed because this time they installed hardware to prevent it instead of just software like the first XBOX. You can buy a cheap mod chip though that will allow windows to be installed on a 360 but it will certainly void any warranty and I would think using any online XBOX services would be pretty tough because all the commercially available mod chips are known to microsoft and they can check your system when you try to log in.
A high level court ruling here in the US said this year though that you do have the legal right to mod any hardware/software you own but that companies do not necessarily have to provide services to modded units.
