In this presentation by MacWorld we are shown how to use FileVault 2 on MacOS X 10.7, Lion. The presentation starts off, "Apple latest Mac operating system, OS X 10.7 Lion includes FileVault 2, the latest version of Apple’s method of file encryption. In this how-to, we'll go through the steps on activating FileVault 2 for your Mac's internal startup drive."
Thanks Ezequiel Cothran for sharing this with me. It is good to read
through everything here to be thoroughly ready to secure your data.
Especially read the comments! Use at your own risk.