It would be pointless to have all these multicore processors and only use 2 cores lols. Depending on the version of windows it can utilize up to 256 cores\threads on a max of two sockets anymore then 2 sockets you will have to get windows server edition. So windows is designed to use as many threads as you can throw at it to maximize its performance.
I just got a q9550 and my task manager says Windows 7 is using all of my cores..
Is this normal? Isn't it supposed to be using only 2?
In the search box, type: performance monitor
Run that app - It'll display the resources the system has and how much is being used. With your 4 core processor, you should see 4 boxes in the CPU section. At idle, those 4 should be pretty much empty. Under use, the traces on the graphs will change to indicate each core's current load. If you see all 4 cores, and there's little/no load when the system's not doing anything - that is proper behavior. If you're not doing anything and all 4 cores show a heavy load - then there may be a problem, and you should investigate what is using your comp.