As far as inexpensive fanless systems go, perhaps consider the VIA Eden platform. It's definitely got the power to play back oggs and mp3s (and maybe a bit more), as well as having some nice integrated goodies (Audio, NIC, USB, etc). To top it all off, I've seen the board/CPU going for $100 USD. It may be just the thing.
As far as inexpensive fanless systems go, perhaps consider the VIA Eden platform. It's definitely got the power to play back oggs and mp3s (and maybe a bit more), as well as having some nice integrated goodies (Audio, NIC, USB, etc). To top it all off, I've seen the board/CPU going for $100 USD. It may be just the thing.