This is directly from a social.technet.microsoft.com from someone who got it working:
I had the same problem (but with a ThinkPad w500) on Win7 RC1. The problem is actually quite simple to solve, once you know where to look of course... ;)
It does not involve Group Policy settings - even though the setting can be controlled via that approach, but its not per default.
Goto: Control Panel\All Control Panel Items\Biometric Devices
Click: Change Biometric Settings
Allow users to log on to Windowsd using their fingerprints
Allow users to log on to a domain using their fingerprints
Restart the computer.
Click: 'Switch user' at the log on screen and choose the fingerprint icon (this of course requires you to first have added a set of fingerprints to your account)
Swipe your finger. At this point nothing happens (or at least it didn't for me). The screen remained active with the fingerprint icon and a password field.
Now type your password and your'e logged on (I guess this i a final security measure to validate the account against the AD).
Now restart your computer and voila! your fingerprint is accepted and password no longer required.
Hope this helpes...