I just recently posted more details about how I use my Nant script to do some pretty complicated things with Nant, but if you want a nice introduction to build files, you should read
Dave Bost's article. It was supposed to be in the May/June issue of
CoDe Magazine, but it
didn't quite make it. Either way, it's online, and is a good resource to get started using Nant to build your projects.