hey boy, good choice you made there to make your own PC rather then off the selve
Personally, i recommend a athlon II 2.9 Ghz X2 chip with like a HD4850.
For case Id say take a antec that comes with 350w PSU. For mobo pick the cheapest asus, gigabyte, foxcon or MSI that suits the AM3 socket.
If you are short on budget you can always just get 2 gb DDR3 instead of 4. Just dont forget to plug in another 2 gb over the summer, when ddr prices generally are lower.