Tell me about wiring LEDs

like, probably at least 50 of them. If anyone on here knows a bit about circuits I could use your advice.

This thread on the ePlaya gave me the idea. Basically, since I love music (playing and listening), I want to arrange a bunch of LEDs on an old shirt, not unlike what that guy's doing, in the shape of a treble clef.

Now, I'm not a complete newbie to electrical circuits, but I'm not exactly an EE major either. I've done basic circuits before for a couple random things, as well as wiring for electric guitars (so I'm comfortable soldering small parts and have all the gear for that).

So, basically, I need to know something about how the circuit should be arraged (I've managed to pick up that I can't wire that kind of amount in series), what kind of power source I'll need (hopefully something that fits in my pocket :P), and anything else you think might be good for me to know.