To install, you just have to copy Nicotine.app from the disk image. While you certainly can install nicotine using Fink, according to Capt'n Swing's tutorial, that's not necessary to use Nicotine.app.
People still seem to be having some trouble with this: To download, you don't just double-click on a search result. You have to command-click on a result, and choose "Download" from the menu that pops up. Sorry it's so difficult.