home made amp and woofer for my car?

I have a crapy stereo system in my car. I have a small guitar amplifier that connects to a power outlet (for a guitar obviously) and i want to hook it up in my car. Now, i know how to hook up the audio, but what about the power??? I though that maybe a inverter would work (the ones from radio shack that connects to your power adapter) like this one http://www.radioshack.com/product/index.jsp?productId=2194429&cp=&sr=1&origkw=inverter&kw=inverter&parentPage=search What do you guys think??? I mean, logically the inverter gives out 120v and it says it can power laptops, small tvs, and even game counsles: but can it run an amp??? Or maybe a set of home speakers with a sub woofer. Im not shure. The inverter is only 50 dollars, but i dont want to waste money on something that wont work. what do you think, will it work?

to tell you the truth i have actually done this
before and its not worth it.
your amp will keep shorting out
and resetting but if you really want to
try it go and buy a power adapter
that plugs into your cigarette lighter
you can get them from radio shack and other
general electronic stores