in a word NO
CD-r discs can only ever be written once, so if your going to write a CD-r you may as well use as mush space as possible as the disc cannot be rewritten to,
CD-RW discs (CD-ReWritable) can be erased (made blank again, ready for reuse)
you can't get the music off the CD-r so it will just play the music
XP media center will probably support UDF (a way of putting stuff on a CD) so a blank CD-r can be written as and when you want (so it will show free space) but it can only be written fully once
basically i only use CD-RW discs, because they can be blanked