Most speakers (front and rear) are 4ohms svc. The subs are mostly 4ohms DVC, althought you can get some that are 3ohms DVC and SVC. With DVCs, it's like having 2 pairs of 4ohms SVC. So the combination would be 8ohms or 2ohms. In all, 100w x 4 amp is for 4 4ohms svc speakers. However, most all amps will support 2ohms in stereo mode. So the 100w x 4 will probably do 150w - 200w x 4 at 2ohms.
So Isaac, to dumb this down a whole lot more(I am used to subs not door speakers) if I get an amp that does 100x4 at 2ohms and is 50x4 at 4ohms, and I hook each channel to a 4ohm speaker, what will I be getting?
If it is the 50 watts, is there a way to get the 100watts out of them anyway?
You will be getting 50w per speaker. If you want 100w x 4, then double up on the speakers (hook 2 4ohms svc speakers in parallel to get 2ohms). If that's not possible, then get 2ohms speakers.