Nullriver’s Connect360 is a fantastic little app that you can run on your Mac that will fool your XBox 360 into thinking its talking to a PC, allowing you to share your iTunes, iPhoto and video libraries with the 360 dashboard. The video transcoding is a little lossy, but for SD applications it works exactly as advertised. Well worth the $20 they’re asking.
According to the Connect360 Support website, you can’t use Connect360 on your Mac to connect to your XBox 360 if your network uses a Linksys WRT54g with homebrew firmware on it. They’re right — it doesn’t work.
The solution is pretty simple, however. Abstract the Mac and the XBox from the router using a good* network switch. The switch will allow the two devices to communicate (via broadcast) with each other without having to go through the router, and all will work as expected.
*Note: The Connect360 site also warns that some switches may cause a similar problem. I’m using a NetGear Gigabit Switch to accomplish this, and it works perfectly. YMMV.