Are there any reasons you want to keep Windows media center as your OS? If you really want to use the mbox, go out and buy a copy of windows xp home edition and do a clean install. You can find plenty of tips and help for setting up windows xp for the mbox at the digidesign site. Look under support and go to the DUC (digidesign user's conference). Doing a few searches should turn up most of the info you need.
If you have already dumped the mbox, or need to keep windows media center as your OS, then I would look at one of the e-mu interfaces. I'm using a 1616m with a Dell Inspiron 9300 and Windows Media Center as my OS. Even before I did the recommended tweaks for audio, I was able to record audio and sequence midi tracks with no hassles. The e-mu stuff is also coming with a lot of nice "lite" versions of major software (cubase, sonar, ableton, etc.) plus it comes with a lite version of the emulator plug-in. All in all, I am very pleased with what all I picked up for the price ($499.99).
If you are brand new to computer recording, you really want to visit forums related to the software you want to use in order to make sure your machine is up to spec and to find out which audio interfaces will work best with it.