HowToForge has a terrific article on how to use the standard Ubuntu installation to create encrypted partitions. Perfect for laptops. Keep in mind, however, that the machine is obviously encrypted using this technique and doesn’t provide plausible deniability should you be asked by law enforcement to decrypt the drive at international borders, etc. If you have a deniability need, check out TrueCrypt instead — though there have been rumblings that TrueCrypt’s obscurity feature isn’t as strong as once thought.
I’d also like to take this time to apologize for being MIA these past couple of months. I’ve been working on a project that’s been taking up all of my time. I know that I still owe you Part III of my KVM series (which covers sound and USB devices) and I’ve got a quick look-see planned for the Hardy Virtual Machine Manager (virtmanager). It’s a good tool, but has limitations. Look for those articles in the next couple of weeks!