a coax (coaxial) is the mid and tweet togetherm typically powered by the same chanel of an amp or deckm with no, or simple capacitor as a low db high pass xover for the tweet.comps (component), are seperate mid and tweet. They can be run either active or passive for the xover, either using one or 2 channels of an amp per side.
Great explanation, man. Co-axials can also be just a full-range speaker that has a tweeter inside the magnet, or something like that. Not really sure of the mechanics behind it. But, the tweet doesn't always have to be mounted ontop of it.
However, components are usually
a lot better quality than coaxials.
And, like he said, co-axials are usually powered by a simple, relatively weak power source, such as a head unit, while components handle more power (The normal is 100 watts RMS), and are normally a lot better sound quality and build quality.
However, don't be afraid to just stay with coaxials. But if you get a strong sub stage, you'll probably want to get a nice pair of components, or a 3-way front stage (mid-low, mid-high, and high drivers) to make the sound quality nice and full, so you can actually hear the song, instead of just hearing bass.
EDIT:: Also, component systems come with a passive-crossover. What this does is, you run a single channel into the + and - of this crossover, then it has pegs for the mid and the high drivers, and it seperates the signals, and send it to the right driver.
