So here I am, trying to meet another deadline and still maintain my sanity by doing something even remotely interesting. I seem to have at least partially resolved my Rendezvous/multicast issue by removing the newfangled Windows P2P "Peer Services", mostly through the age-old process of Windows troubleshooting: Uninstall suspicious stuff, reboot, lather, rinse, repeat.
Among the suspects that fell into the bit bucket by the wayside were Visual C# 2005 Express Edition (the last thing I installed before my performance counters vanished), the Cisco VPN Client (I use it on a daily basis, so I know how flaky and godawful intrusive it can be), WinPCap, the custom TAP driver installed by coLinux (which got uninstalled too), a couple of Toshiba drivers I never much liked the look of, UPNP support, and, of course, the "Peer Services" thing, which got installed along with SP2.
I got so monumentally fed up with Windows that I put the laptop away out of sight, retreated into my iMac, and thanks to an updated version of Desktop Manager, am now getting some real work done on a glorious 4x20" virtual desktop. Of course I still need Visio (I have a lot of effort put into several detailed diagrams), so I pulled out Remote Desktop and hooked it to my laptop (the only way it was going to get a 20" screen). Utterly ridiculous, the fact that I can't use ClearType on top of a 100Mbps connection, but hey, it works.
So, right about now, I have MSN, Skype, iTunes, Mail.app, Word, PowerPoint, NewsFire (which turned out to be great for streams of del.icio.us items and Google News feeds - the sort of thing I might want to look at but not keep or forward), Safari and a bunch of terminal windows in a couple of desktops, and two full-screen displays to my Linux and Windows boxes. All working smoothly.
Gratuituous Safari hint: If you want to tile windows neatly (say two windows on a wide screen), resize one window to half the screen size and do a Cmd-N. Presto, an identical-sized clone.