The MS site has some good info, take alook at click here, 'Optimizing Windows XP Media Center Edition 2005, Xbox 360 and Media Center Extender Networks'
Also, the FAQ: Media Center and Xbox 360 may be of some help, click here. 2 questions seem appro. to your Q;
Do I need to install Update Rollup 2 on my PC running Windows XP Media Center Edition 2005 for my Xbox 360 to be able to connect to it?
Yes, it is easy to download Update Rollup 2 for Windows XP Media Center Edition 2005. Update Rollup 2 also includes other new features. You can also visit click here to download all of the necessary software. You must download to a PC running Microsoft Windows XP Media Center Edition 2005.
Do I need to install any other programs to make the connection between my Media Center PC and Xbox 360?
Yes, there is a software connection program that you will need to run on your Media Center PC. Once you have set up your Xbox 360, follow the onscreen instructions for connecting to your Xbox 360. You can see a preview of the process or you can visit click here to get started.
Hope this helps.