What do i need to use to encrypt my usb hdd?

Question

I want to encrypt my USB HDD. And

i want to do it with open source software. And

i want to use only password for decryption. And

i want to decrypt it using an Ubuntu 10.04 LiveCD, with no internet-connection. And

i don't want solutions using e.g.: DES with 56 bit. At least AES 256 bit please!

What is the solution?

Thank you!