Insert your Mac OS X disc and then power on the computer, once your hear the "bong" sound hold down the "c" key until it presents you with the Mac OS X language selection screen. From there it is pretty straightforward to install the OS
Go to the Utilities menu and open Disk Utility. Your drive should show up on the left. Click it and hit Erase then format with HFS+, journaling doesn't really matter. Format.
Load the OS X DVD as already said, and open Disk Utility. If this is a brand new drive you installed, most likely it has no partition scheme, so you will need to set a partition scheme before you can format it. To do this, follow the directions after opening Disk Utility:
After you complete the these steps, you can close Disk Utility and continue installing OS X.
Thank you everyone so much. I'm a first time Mac user with little knowledge of the OS besides basic functions so I was really stuck. Now I am happily running my laptop with 4 Gb RAM and a 500Gb HD! Thanks, and happy Mac-ing!