Perhaps slightly off-topic, but here goes..
If your only interested in the MP3 playback (not photos), and don't already have a 2nd Gen Tivo, you might consider a different bit of hardware: the SliMP3 -
http://www.slimp3.com/index.html
The SliMP3 is a dedicated mp3 head-end for an audio system that'll play both mp3's and shoutcast-style mp3 streams over the internet. The server software is written in perl (GPL) and runs on just about any platform you want (including MacOSX). The player is autoconfiguring if you've got dhcp somewhere on your home network (most NAT's do this now), and will auto-discover the server and establish comm's with it automatically, very similar to Rendezvous. Of course, this can all be overridden manually, if you want.
What's really cool about the server software is that it will also stream to iTunes, allowing remote-control (from the server's web-based management tool) of multiple mp3 players, whether they be SliMP3, XMMS, iTunes, WinAmp, etc. I'm using the server software with iTunes right now as I await the arrival of my SliMP3 player. It's a nice way to 'test drive' the server software.
The cost - $250. Of course, this might inch up a bit if you have to run ethernet to your stereo system, or if you choose to go
wireless , but you're gonna have this cost anyway with the TiVo solution. Also, with the TiVo, you'll have to get a USB-ethernet adaptor for it when the time comes; there is not a native ethernet connection on the TiVo2.
The best part (to me) is that both the server software and the communications protocols are completely open. Adding functionality to the server is not only possible, but encouraged.
BTW, I have a first-gen TiVo and I love it. The 2nd gen's look really nice, but I just don't watch enough TV to justify it. So, don't get the idea that I'm slamming TiVo; I'm not (Tivo/RV sound really cool). Just offering an alternative.