Reinstalling Mac OS X on Macbook with swapped hard drive? I don't know much about Macs, so when my girlfriend asked me to repair her old Macbook, I tried to swap out the hard drive from my junker laptop. I got it all changed and now the boot manager shows a single partition for Windows. However, I am a little stuck on how I am to boot into Mac OS X to reinstall it?

I was able to get a dump of the App Store version of Mac OS X Lion, and upon placing that on a USB drive with TransMac, it was recognized by the boot manager. But unfortunately, on choosing it, a large NO symbol was shown and the computer shut down.
This question has been answered here. 

Basically do the following:

To start Recovery, hold down the Command + R keys while booting. The interface is pretty straightforward after that and you should be able to figure it out.