I'd suggest going with the Intel Core 2 Duo E8400 processor for $170.
For a graphics card get an ATI 4850. They are currently the card with the "best bang for the buck". Here's a link to a good one http://www.newegg.com/Product/Product.aspx...N82E16814102747
I would spend around $100 for a decent Intel motherboard. Some good brands for motherboards include: Asus, Gigabyte, and MSI.
For the Hard Drive, 500gb is currently one of the best price per gigabyte points. You can usually find them for around $75-$80.
4gb of ram is a good amount of ram, but if you're running low on cash, 2gb should be enough for now. I'm running 2gb and don't really notice any sluggish activities, except when installing large programs or games. You will need a 64-bit OS for your computer to recognize more than about 3.5gb of total ram.
For a power supply you should get something around 400 watts or better. I'd suggest this one: http://www.newegg.com/Product/Product.aspx...N82E16817371007
If you need more help, feel free to ask!
"I think there is a world market for maybe five computers." - Thomas Watson, Chairman of IBM, 1943