Anybody can find the software by searching on google or similar. For instance, search for "open source fingerprint software" or "free fingerprint biometric software". There are many options available, and the choice of which you use will depend on your needs. For a "very simple" one, like you said, you could use a demo version of a commercial biometric product, say if you just need something to prove a concept. For more complete projects, you might look at something like
http://sourceforge.net/projects/fvs/, which is open source.
Since you've just said you need a "very simple fingerprint identification circuit" but not provided any details, that's probably about as much as I can help. You'll have to do some searching and some reading, and decide what options best suit your needs.
Is this for a school project?
How you get the result from the software depends upon the software. In the case of the open source stuff, you would A) hope it can provide an output via, say, a serial port, or B) if it doesn't, modify it so that it does.
I meant "hack" in the original sense, not the media's messed-up criminal sense. Definition 1 from the Jargon File (
http://catb.org/jargon/html/H/hack.html) covers it best:
hack
[very common]
1. n. Originally, a quick job that produces what is needed, but not well.
Torben