The AnandTech Linux XBOX PC Experiment
 

As you can see, it's pretty difficult to get a cheap AMD or Celeron system in the fray (cost includes case, CPU, motherboard, memory, hard drive, DVD Player and cooling). All configurations use integrated video. The Semprons and Celerons are going to be much faster than our 733MHz XBOX, although the footprints on the Sempron and Celeron setups are pretty terrible - they take up the full space of a mid-ATX case. The XBOX is also the significantly quieter solution. Unfortunately, the XBOX has very little memory and when we fire X, the XBOX is really going to take a hit in performance

http://www.anandtech.com/linux/showdoc.aspx?i=2271&p=1