1. If you haven't disabled Aero, do it
Done it allready

2. Consider upgrading to Windows 7. The Release Candidate is free until next year. Big performance improvement for HDD, etc
Had one, but it only worked for a month. Might take this new one then.

4. Definitely set CPU affinity. Rotate cores.
Got them set to "all", so far it seems to run best. I can decendly run around dalaran with 7-12fps on my main.

5. Drop graphics to minimal
My main has all details on, all but shadow which is around 40%. The 4 others are on lowest possible

6. Make sure in the WoW Video Options, Resolution pane, "Multisampling" is set to someting with 1x multisampling (e.g. 24-bit color 24-bit depth 1x multisample)
Allready set

Somehow when I set my affinity to "all" it starts using 100% cpu in dalaran and outside dalaran a little less. Seems a bit much concidering that my CPU should be powerfull enough for it.

The game gives me 10fps extra in dalaran and a lot more smoothness outside dalaran when don`t use window mode for my main but then I cannot move to the other clients in my second screen.