ok, so this is going to sound really vague, but i need some help. i have been playing shows for quite some time, but i have my first one for a large audience coming up, and i am playing an acoustic part. now usually i would hook up a mic and play into that, but this "act" we are doing involves quite a bit of moving. so here is the question:

i saw this thing that goes under the strings of an acoustic that sends the sounds to a nearby amp, but i dont know what it is called. what is it, and where could i find something like this. thanks much
that's a magnetic acoustic guitar soundhole pickup you are talking about. Try ebay or seymour-duncan site. I know that a used seymour-duncan costs about 40 dollars.
you can find acoustic pickups anywhere...ebay has alot of good deals. Just find one that pops into the soundhole and you're set.
But know this: Plugging an acoustic guitar into a regular guitar amp does NOT sound good. It's a known fact the two do not accompany each other well. They make amplifiers specifically for acoustics to handle the frequencies that the guitar puts out. Most acoustic amps have a regular speaker plus a tweeter. There is a solution, however:
If you're playing out and you use a PA system, find a way to plug the acoustic directly to the soundboard. Then the soundman can tweak your EQ settings and the speakers you play out thru have....guess what? A speaker and a horn, essentially a larger tweeter. The sound you get this way is unbelieveable.