Take a look at Impact of Artificial "Gummy" Fingers on Fingerprint Systems. Tsutomu Matsumoto; Proceedings of SPIE Vol. 4677 (2002)
Matsumoto gives a pretty simple method for attacking fingerprint scanners and achieved really high success rates on all 11 scanners he tested. It is hard to tell from the paper if the scanners he tested were just consumer level devices or something that is meant to be used in more secure situations.