do you mean that you have a $500-$600 budget for just those 4 parts? (mobo, cpu, psu, os) or $500-$600 for the whole thing?
for the cpu and mobo, that deal with the 940 and the biostar is good. i doubt you will have problems installing the os, they are a good brand.
don't go with the old phenoms, the phenom II's are much better. the old phenoms are the old 65nm chips that use up more power, have less performance, and produce more heat. stick with the phen II's.
if you feel you don't need quad core power, you can always get a phenom II x3 with three cores. this looks to be a good combo.
Newegg.com - Computer Parts, PC Components, Laptop Computers, Digital Cameras and more!
also for the psu, this is a good one.
Newegg.com - Antec Basiq BP500U 500W Continuous Power ATX12V Version 2.01 Active PFC Power Supply - Power Supplies
and for your OS, save your money from vista, and get the windows 7 RC
the full windows 7 will be released this october, so you can use this until then and then purchase the full, wouldnt be worth buying vista now.