transferring files from pc to xbox and back will probably require a mod chip...you can download stuff from xbox live and you can transfer music file onto the xbox from your PC but the xbox does not support a lot of file transferral
While we are on the HD-DVD subject I just picked this up to replace my old Marantz DVD player
http://reviews.cnet.com/8301-12760_7-9672294-5.html
It is great...and I love that it covers all of the formats and still costs the same as either a bluray or HDdvd player