Nullriver software has some great shareware products. I have used PSPWare to manage my PSP since it came out. Another Mac app from Nullriver that lets you manage media is Connect360, this time connecting your Mac to an Xbox 360.
As with PSPWare, Connect360 ties iTunes and iPhoto to the console seamlessly. This works over a wired or wireless network. Both the Mac and Xbox 360 need to use the same network however (both wired, or both wireless, not mixed).
Connect360 is actually a Preference Pane in System Preferences, and also includes a Menu Item for easy access. It uses a background application, Connect360Helper, which uses less than one percent of my CPU.
Just for reference purposes, I am using a dual 2.5 GHz G5 with 3 GB of RAM. There is no hit on system performance at all. Of course your mileage may vary dependent on both the speed of your Mac, and the speed and congestion of your network.
Once you confirm that your Mac is talking to your Xbox 360, (you get an audio cue by default) everything is done on the 360 itself. You can access computers on the network from the System Blade, Computers page, but this is not necessary.
From the Media Blade, select either Music or Photos. From here select Computer, answer Yes when prompted about Windows Media Connect, and the 360 should find your Mac on the network. Select your Mac, and that's it — no more configuration needed.
Your Xbox 360 understands playlists in both iPhoto and iTunes. You can also view music by Album and Artist, which lists everything in your iTunes Library. Connect360 also supports streaming of live Internet radio broadcasts to your Xbox 360, such as Shoutcast. Just make a playlist with all the radio stations.