
Vista tells you it needs a TPM for BitLocker, but it lies. Follow these steps to enable BitLocker without a TPM:
1. Open the group policy editor by clicking Start, typing gpedit.msc, and then pressing Enter.
2. Navigate to Computer Configuration\Administrative Templates\Windows Components\BitLocker Drive Encryption.
3. Double-click Control Panel Setup: Enable Advanced Startup Options.
4. Click Enable. Then, select the Allow BitLocker Without A Compatible TPM checkbox.

5. Click OK.
Now, you can enable BitLocker without a TPM.
http://www.vistaclues.com/enable-bitlocker-without-a-tpm/