i can answer your question about the alternator...

it's under your hood and it is connected to your engine via a belt and basically when your engine turns it spins the alternator thus producing all the electrical power for your car. like a mini generator. well, sort of...

 

capacitors store power, kind of like a battery, and you put one inline with the amp so it can draw large bursts of power from the CAP. when it is needed. Like on hard bass hits

 

so for an amp throwin 500watts consistantly a capacitor is recommended?
and - how much would the alternator upgrade cost me?

 

if you have access to an auto shop like i do, it wil only cost you the price of the alternator. I am fortunate to live on an air force base where we have a fully equiped auto hobby shop. only $2.50 an hour for a stall. and you can use any and everything you want. if you want prices on alternators just look on the internet or call your local shop. if you dont have access to a shop/tools then you are looking at like $40-$60 an hour for labor and since most places go by a book that tells them how many hours it "should" take, you might be looking at no less than one hour and no more than (my guess) 2 hours of labor.

 

start with the altinater. you only need to upgrade it if it becomes a facter. which in most cases it wont. unless you gong to be pushing over 1000 watts of power. as for the cost it all depends on what you go with and how much you want it to put it out. look to spend no less then a $100.
as for a capacitor, you only need one if you notice your head lights dimming at night when it hits a good bass note. some say no but its disputible. what it really does is takes a lot of stress off you battery. when you amp hits it draws from the battery. with a cap in line with the battery it draws from the cap first which also reacts faster then the battery. easy terms you get a lot better bass response. i would recomend getting one if your bass amp pushes over 500 watts or 700 watts total power all amps.