FWIW, I had iTunes 220.127.116.11 already on my WinXP system, and I decided to try it as a server for my M1001. I have not had any issues yet. It took iTunes awhile to build its database of my 11000+ files (getting album information, etc.), but after that, iTunes starts up in about 10 seconds on my test server.
The Roku found it right away and seems to be able to browse pretty quickly.
I'm using iTunes 7.5 on my Macs here (3 of them, all Intel running 10.4.10) with no problems at all. Also, my Soundbridge (M1001, latest beta firmware, connected wirelessly) is working fine with iTunes 7.5.