CPU: i5 2500k ($220 on Newegg)
MoBo: ASUS P8P67 PRO (about $178 with shipping on Newegg)
RAM: I honestly think 4GB is enough (especialy if it is at 1.6GHz)
OS: I would recommend getting Windows 7 if you are willing to change your OS (Vista is a RAM whore) for $95 on Newegg.
You'll have $50 left which you can spend on whatever you want
I read somwhere that the 5850 requiered atleast an 500W PSU, Does this affect performance? Because my pc never just turns off or other problems like that, and I thought that was pretty common when you're PSU were this weak...
Anyway, any good PSU's that's cheap and worth the money?
Don't know what to look for, when it comes to specs etc.
Correction, you will need a 500W PSU or more. You can easily find one for under $75 though. I was looking at an old graph with older hardware. Although I doubt your system will reach 500W at full load, it's safe to have some extra wattage around to stay on the safe side.