The one posted from Best Buy will NOT work for a gaming laptop at all.
Stay away from Dell, E-machines (which is Dell), and Gateways. These machines will generally not hold up for a serious gamer.
I second (third? lol) the use of Newegg to seach for a new machine. They are currently running a few sales including discounts and free shipping on select items. Newegg is also wonderful because it's spec pages are very detailed!
Personally I would get an Asus or maybe a Vaio. Asus is considered one of the best companies out there amongst those who work with computers. It's been around forever and also makes computer hardware.
You need a duel core processor at least... not sure if laptops are up to quad yet. 2GB of ram at the minimum. A dedicated video card would also be needed for gaming... integrated would not have the dedicated power and memory to play the VAST majority of games.
To be 100% honest... I am not sure you will find anything under $500 that would be considered a gaming laptop. Most likely you would be at $700+. You may get lucky and find a deal this time of year though, so don't give up.
Note: This advice is my own as a gamer. I play/have played EQ, WoW, Dawn of War, Guild Wars, Sim City 4, and the Civilization games (plus more).