Welcome to the Apple Support Communities
If you have a Mid 2007 or newer MacBook Pro, you can use OS X Mountain Lion. Buy Snow Leopard > http://store.apple.com/us/product/MC573/mac-os-x-106-snow-leopard Then, make a backup, insert the DVD and upgrade. Finally, open > Software Update to install the most recent version.
Open App Store and purchase Mountain Lion. Check if your apps are supported > http://www.roaringapps.com