Integrated Fingerprint Reader
IBM released a second generation of T42 models in autumn 2004 featuring Intel Pentium M 765 processors and an integrated fingerprint reader.
The fingerprint reader is produced by a company called UPEK, which is specialized to fingerprint readers.
It seems to be integrated as a USB device.
Furthermore, IBM states that there's an interface with the Embedded Security Subsystem.
Linux Support
Nothing is known so far about if it's supported under Linux or not.