Not to be rude, but as john123 said, $500 won't get you far at all for games. If you're into building your own, I have some parts I can recommend, but you'll have to use either some old speakers or the monitor's integrated speakers. I got pretty much everything that's the cheapest on Newegg, disregarding speakers, and it still came out to $522. Here's the configuration I did...may not be the best config for $500, someone can probably do better that I did.
Case: COOLMAX CV-560
http://www.newegg.com/Product/Product.asp?Item=N82E16811212028
Mobo: Foxconn NF4SK8AA-8KRS Mobo
http://www.newegg.com/Product/Product.asp?Item=N82E16813186059
CPU: AMD Athlon 64 3000+ Venice
http://www.newegg.com/Product/Product.asp?Item=N82E16819103537
RAM: Patriot Extreme Performance 512MB
http://www.newegg.com/Product/Product.asp?Item=N82E16820220018
Video Card: GECUBE GC-RX700G2-D3 Radeon X700
http://www.newegg.com/Product/Product.asp?Item=N82E16814241024
Hard Drive: Seagate Barracuda 7200.9 ST3120814A 120GB
http://www.newegg.com/Product/Product.asp?Item=N82E16822148104
PSU: Rosewill RV400-2 ATX 2.01 400W PSU
http://www.newegg.com/Product/Product.asp?Item=N82E16817182014
Monitor: Viewsonic Optiquest Q7B 17 inch
http://www.newegg.com/Product/Product.asp?Item=N82E16824116010
Don't get me wrong, this really should be a huge gain from your laptop, but it definitely won't play any new games at full graphics settings.
It's also not really a pretty looking case; it's very, very cheap. Not sure about quality either.
Also, I think you'll need SATA connectors with the hard drive.
http://www.newegg.com/Product/Product.asp?Item=N82E16812104655
That'll bring the cost to $530, $8 more.
Plus, you may need some case fans. It comes with 1, which may be enough if you're not overclocking. But if temperatures get high, you'll probably want to consider getting some more.
