[Olds64]

You can always spray the hell out of it with starting fluid. If the idle changes then you know you have a vacuum leak.

Or if you smoke you can take a BIG OL' HIT... er I mean... DRAG and then blow the smoke into one of the vacuum lines with the engine off and see where the smoke pours out of your intake / carburetor. (NOTE: this might not work too well since most people couldn't inhale enough smoke to make it noticable when you blow it into an engine). If you are really intent on using the smoke idea then there is a machine called a Vac U Tec that does that with a little electric heating element that burns STUFF to make smoke. They are fun to use.