Kari, your Macbook Pro will support the latest Mac OS X 10.8 Mountaion Lion. Unfortunately, Apple doesn't release any bootable DVDs or USB Drives for Mac OS X 10.8 Mountaion Lion. So, there is no way to install 10.8 Mountaion Lion directly. But there is an alternate way.
You can buy the Mac OS X 10.6 Snow Leopard Retail DVD
($19.99), and install it first. Once you installed 10.6 Snow Leopard disc, just update it to it's final version i.e 10.6.8 through Apple menu > Software Update option.
Then you can buy and download the latest 10.8 Mountaion Lion ($19.99) from the AppStore application in Snow Leopard (there is an application named AppStore on 10.6.8 Snow Leopard where you can buy or download applications from Apple as digital download)
You can buy Snow Leopard Retail discs from Apple, eBay.com, Amazon.com etc
See here : http://store.apple.com/us/product/MC573Z/A/mac-os-x-106-snow-leopard
Once you get the discs, all you have to do is put it to your Mac, restart your Mac and immediately hold down C key on your Keyboard. This will boot your Mac into the installation DVD, then follow the onscreen instructions to install the Mac OS X.
If you've any questions or would like any additional information, please don't hesitate to ask.