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 ConfigurationAdministrative TemplatesWindows ComponentsBitLocker 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.