Things you need for modern games...
processor - most likely a dual core
hdd - something with at least 80 gb and 7200rpm
enough ram - at least 1 gb nowadays
graphics card - something that is non integrated (im not too knowledgable on this area. other guys will be able to fill you in more). Most new laptops under 900 will have an integrated graphics card though.
With this you will be able to play modern games fairly well. These are just the basic key components though.