Use Vista’s BitLocker with a USB Key
Vista’s BitLocker drive encryption is available in the Ultimate and Enterprise editions. To use it, you’ll need a computer with a supported Trusted Platform Module (TPM), but even if you have one, it may not be enabled properly in your computer (in which case, you’ll be waiting on your PC or motherboard vendor to update the BIOS).
You may remember some talk about Vista allowing you to use a USB flash drive on systems that don’t have a TPM. It’s possible, but you need to dig up an obscure setting to turn it on.
This is an excellent walk through for anyone who wants to use BitLocker in Windows Vista, but might not have a TPM (Trusted Platform Module) equipped computer. Keep in mind, this is only available to those individuals with Vista Enterprise and Vista Ultimate. This shows you how to store your encryption key on an ordinary USB thumb drive. It has all kinds of pretty pictures so you shouldn’t get confused while doing this. 
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