um actually... different drives have different success rates with cd-rs and cd-rws. You could get a different xbox revision or "generation", and depending on the drive you might get cd-rs to work. I have a launch revision 1 xbox and cd-rs never work. On the other hand my friend just got one a few months ago, and some cd-rs work on his xbox. Microsoft initally made the systems with drives that wouldnt read burned cd's but apparently things changed. Like I said it is a HARDWARE issue. I'm not trying to pick a fight I'm just stating a fact.
edit: to elaborate further, there are three main drives used, a thompson, a philips, and a samsung. The thompsons suck *** and sometimes dont even work with regular game discs(stupid errors). The phillips is better, but still has trouble with cd-rs. Apparently xboxs with the samsung drive can read cd-rs fine. It isnt an os issue.