I chose the wrong partition to install Windows. How do I reinstall Mountain Lion? I've had my new Mac for less than a week, and screwed it up.  In trying to create a dual boot, I made noob mistake in choosing the wrong partition to format to NTFS for Windows (the partition with boot camp).

The good news is that looks like Mountian Lion is available in the AppStore for download.  The bad new is I don't have a Mac OSX to download.   I'm pretty sure the recovery partition still exists, but I don't know how to access it at this point.  What can I do?
You can boot into Recovery Mode by following the instructions outlined in HT4718 and re-install OS X from there:


  OS X Lion or OS X Mountain Lion includes a built in set of utilities in the Recovery System. Restart your Mac and hold down the Command key and the R key (Command-R), and keep holding them until the Apple icon appears, indicating that your Mac is starting up. After the Recovery System is finished starting up, you should see a desktop with a OS X menu bar and a "Mac OS X Utilities" application window. Note: If you see a login window or your own desktop and icons, it is possible that you didn't hold Command-R early enough. Restart and try again.