Very easy to reprogram. Use the same program you used to program it initially.
Start->All Programs->Access IBM->IBM Fingerprint Software->Control Center
Fingerprint reader is very sensitive to angle of finger, but there could be other things as well. Greasy, dirty, or wet fingers could have an effect. (But you don't want to get those all over your Thinkpad anyway, so I'm sure you washed with soap and water, right?

) I found that I initially programmed my index finger in at an awkward angle 'cause I did it lying in bed instead of sitting at a desk.
Thinkpad T43p 2668H2U - Pent M 770 (2.13) - 15" UXGA - 60GB 7200rpm HDD - 1GB SDRAM - DVD Writer - Intel 2200bg - Fingerprint - Bluetooth - 9 cell battery