You can try the Pos .Net, but finding compatible hardware is a problem.
You can also look for drivers and devices that support the bioapi (
www.bioapi.org) spec and see if you can write code directly against them.
Otherwise there are several third party specific SDK's that you can use.
www.coding4fun.com has a sample app that uses the MS finger print reader via one of these SDK's (griaule ?). The link to the specific article is;
http://blogs.msdn.com/coding4fun/archive/2007/03/06/1815291.aspxSadly, this is not an easy thing to do (in general), especially if you want to support a range of hardware.