4 ch amp, 2 component 2 ohm, 1 sw 4 ohm

I just bought a pair of components and a sub from a friend.  He threw in a 4 channel amp as well.  I'm not really looking for perfection, but wanted to upgrade the sound a bit.  I'm just unsure about the amp hookup.  I've installed a few systems with all speakers having the same impedance.  This system will have two component sets (rated at 2 ohms a piece - (the 6.5 woofer reads 2.8ohm and the tweeter reads 3.2 )) and one 10 " sw unless I can hook something else to the fourth channel.

I assume each comp set will run at two ohms on the front two channels of the amp.  I wanted to add the woofer on the rear side, but it runs at 4 ohms. 

I'm worried too much about the actual install, but wondered if this hookup will this create any problems with the amplifier.

Also, when installing the crossovers; should I install them before the amp, or after the signal comes out?  Unfortunately, they aren't RCA-wired, they have screw terminals, but I can work with that. 

Can you please specify which amplifier, which subwoofer and which components are you talking about ?

Usually in this kind of a setup, Front channels take the components (you need to be sure your amp is 2ohm stable stereo) and the rear 2 channels are bridged and wired up to the subwoofer.

Thats how im running my setup too.

It's a boss rev-1000 ( says 200 rms per channel/400 max).  I don't believe the numbers, but I shouldn't need too much to push the speakers.

The front channels will take care of the components.  The rear will handle the sw.  I was also wondering about a 3rd speaker, say a 6x9 to fill from the rear.  This would ruin the bridging though unless I use another crossover.

The components are are a pair of 6.5" infinity reference 6020cs (2 crossovers included).  They handle 90 rms @ 2 ohms.   The sub is an mtx 10" @ 200 rms ( I think 4 ohm).

If I bridge the amp for the sub, will that be running down to two ohms?  I assume that would solve it.

If you know anything about the crossovers, let me know.  I've seen many diagrams show the crossover before the amplifier, which would mean the amp wouldn't waste power amplifying power that was shielded out anyway, but I'd need to use all four channels just for the speakers.  Two for the woofers and two for the tweeters.  Then the input would come in already filtered, but I may lose the sub.  Know anything about the power ratings of the crossover?  I doubt I'm going to blow too much with this system, but I'd hate to ruin the crossovers with an incorrect install.

Oh, to clear up the amp installation:

The sub is 4ohm by the way....

I would hook the components into the front (needing 90 rms) and bridge the woofer (if that would work), which needs 200rms.  Would bridging it give the woofer  2 times the power the components get?  This seems like it would work perfectly as I turn up the volume.....

I know that may be a very simplistic interpretation...those usually tend to be wrong.

Any thoughts????