I'd go for the 720 tri core phenom II, just for the energy savings. The 940 is an energy pig. I would also download Windows 7 RC for free while you can still get it. I like it better than vista. It's good for a year. Then you can decide whether it's worth a premium or get vista later.
will a x3 be noticeably slower than the x4 cuz i usually have alot of programs running at once. arent there some compatibilyty issues with windows 7? to install win7 on a new pc do i just burn it on a dvd and install it?
Windows 7 works fine with all my stuff. It found all my devices, and required fewer security updates. Go with the 64 bit version. You can also download a free trial of windows xp that works with windows 7 for using old files that only work with xp. It took me about 5 hours to download the file using dsl, and 20 minutes to burn a dvd using an iso software file I found doing a search online. The phenom 720 won't be that much slower than the 940, and overclocks well. It only uses 95 watts and works with more motherboards. Some boards don't run well with the 125 watt 940.