Aha... a way to find out is to think of a note, sing it, then play it on an instrument (preferably a piano). That's one part of perfect pitch.
The other part is being able to identify notes by ear. Assuming there's a piano or keyboard available, randomly pick a note WITHOUT LOOKING, then identify it. If you identified it correctly, you have perfect pitch. (Well... that's the way that my teacher tested me for it when she thought I had it xP)