With under $500, you can get a good laptop with basic features and average performance when it comes to some games. However, with that kind of money, you cannot get a great laptop for gaming. On the whole, you might want to look into the HP Pavilion g6-2210us, HP Pavilion g7-2238nr, or the Sony VAIO E11 Series SVE11125CXW.
You can fix and old laptop for half that. There are even instructions on the internet. Basically, 2 things are important for the speed of a laptop. One is memory and the other is the hard drive. An SSD hard drive would do wonders and is expensive. A memory upgrade is about $100 and you will need to know the maximum capacity and speed for your laptop. If the motherboard is shot, you can mail your laptop to some places that will fix replace it for about $250. A little research goes a long way.