encrypting a USB hard drive

[thePh@r@oh]

I use a Cavalry 500Gb external hard drive to store material on. I would like to encrypt the drive. Can I do it with stuff still saved on it? Will I have to move stuff off? What solid opensource software is there to help me achieve this?

[KarmaKiller]

TrueCrypt - Free Open-Source On-The-Fly Disk Encryption Software for Windows Vista/XP, Mac OS X and Linux
This is the only one I've ever used, but it's done the job beautifully.

[thePh@r@oh]

yea i heard about this encrypter on Hak5. I don't have to take my files off the disk I'm assuming.