Intel core 2 duo E6300 - $166
http://www.newegg.com/Product/Product.aspx?Item=N82E16819115005
2 gb kingston ddr2 533 - $74
http://www.newegg.com/Product/Product.aspx?Item=N82E16820144157
BFG 6600GT - $43 (after rebates)
http://www.newegg.com/Product/Product.aspx?Item=N82E16814143084
Hitachi Deskstar 250GB - $60
http://www.newegg.com/Product/Product.aspx?Item=N82E16822145087
Asus p5b - $139
http://www.newegg.com/Product/Product.aspx?Item=N82E16813131177
from what I have heard this mobo is awesome, it's a bit expensive though.
Antec case with 400W PSU - $95
http://www.newegg.com/Product/Product.aspx?Item=N82E16811129163
has a good psu (usually case+psu combos have a crappy psu)
Total: $577 + shipping
then add a dvd burner (around $30 probably), a mouse ($10) & keyboard ($10) and you still have $200 left for something I must have forgotten.
In case I didn't forget anything (not very likely, I'm both tired and sick) you could get a better cpu, though the E6300 should be more than good enough for your needs.
Ohh yes, and an operating system. I'm gonna be honest with you and say that just get your hands on windows xp for free. But if you wish to buy it it's probably around $150 for an OEM license.
Ohh and one more thing. That is a pretty decent computer, designed for everyday use + some light gaming. The 6600GT is an ok video card, it's nothing great but you can play most (if not all) modern games on it with low graphics. And a dedicated video card is a must if you are playing games, the integrated ones just aren't powerfull enough.
And I'm sorry if I don't make any sence or if I forgot some parts, as I said I'm both tired and sick at the moment so I'll blame those 2 things for my mistakes.