This is just a brief roundup of what I have found, and what has worked for me for streaming to my PS3.
The XP side of things
I've had luck with the following:
I personally don't trust WMP11, I use WMP10, so I had to find the standalone version of Windows Media Connect that works with WMP10. Some googling did the trick. Note that Hi-def program stream stutters over 802.11 connection I am using.
On the Mac side of things
I found this:
This basically is how to setup the FOSS package called Mediatomb for use on your Mac. If you already use the Fink package management system on your Mac, this is a lot easier. If not, this still walks you through.
Sorry for the short post, but I figure this will help some people out.