With a computer without a TPM1.2 compliant security chip, when you run BitLocker, a warning message will be displayed "A TPM was not found. A TPM is required to turn on BitLocker. If your computer has a TPM, then contact the computer manufacturer for BitLocker-compatible BIOS."
With a computer with a TPM1.2 compliant security chip, when you run BitLocker, there is no screen to save "Startup key" in the USB drive in the wizard.
Systems that support BitLocker Drive Encryption with either TPM 1.2 or USB 2.0 flash drive and are running Windows Vista:
ThinkPad T60, T60p
ThinkPad X60, X60s, X60 Tablet
ThinkPad Z61m, Z61p, Z61t
Systems that support BitLocker Drive Encryption without TPM 1.2, only with USB 2.0 flash drive