Thx for the answers
The processor affinity? Is it a WoW Setting somewhere or system setting? Usually games (like UT3 - which is running in 1900x1200 max details fast like lightning) use all 4 cores as i can see in the display of my G15 Keyboard.

Well the problem is the multi-windowing i guess. As soon as i run just one window, its relative fast with around 80 fps, for every window i open it drops about 20 fps on the main window - with 20 fps left if all 5 windows are open. Main window 1600x1200 and 4 x 800x600 minimum settings. On the 800ish windows i get 50 fps each so it mostly influences the main window ... btw no difference if i use one monitor or both - and on my old pc, it was running much smoother - so i guess its really a OS or driver-issue and for sure not a hardware issue.

I think i will skip Vista 64 for WoW (as long as its not even supported by Blizzard, duh) and will make a new partition and use a 32 Bit OS instead. Now i like Vista - should i stay safe and put XP there or try Vista 32 Bit?! I hate not to use 8 GB Ram and fall back to like 3-4 in 32 Bit .. .but for WoW i have no choise.