Recognizing a person's voice using C#

Basically, you'd need some sort of biometric API \ Voice analysis

You'd need to record the wav file, then store that in the database against a user account.

Then, when user wants to log on, record the new audio from a microphone at the terminal, send that to some sort of service that compares the new recording agaist the database version and performs spectral analysis matching of the 2 recordings.

This really isn't a small requirment!

However, some tools that may help you

http://www.exocortex.org/dsp/[^]

Speech recognition using exocortex

http://www.generation5.org/content/2004/noReco.asp[^]

Update:
What you are talking about is a biometric logon by using voice print audio.

E.g. Say the logon was 'password' for User 1, if User 1 said 'password' and User 2 said 'password', their voice prints would be different enough so that only User 1 would actually get logged on

The second link I posted is doing a lot of this. You'd need to create a spectrogram [^] to perform the analysis.

There's no quick or easy answer to this. You've got some serious coding to do!

Please have visit here to get a grasp of the concepts behind Speaker Recognition[^]. There are different approaches for text-dependant as well as text-independant recognition schemes.
If the system is to be used for authentication in a commercial product you intend to sell, I'd advise you NOT to go for something homegrown, but rather evaluate the biometrical software that is on the market. I also deem it unwise to rely on one biometrical method alone. A combination of two or more might be a better fit. All of this depends of course on what assets you're trying to protect.

Best Regards,