So go to this guys site.....this will get you well on your way......hardest part for me was removing the "plate" behind the door handle.......start in upper left corner(by lock-flipper thingy) with flathead screwdriver. After screws are out.....start in lower, forward corners(down by speakers)....will require a quick TUG and it will be kinda loud....but they come off pretty easy after that. I would also recommend having someone around when you do this step because trying to hold the door you just popped off and also trying to unplug the three connectors that go to the window, lock and door light is a PAIN.....do-able....but a pain.
http://people.clarkson.edu/~calisec/4runner/4runner2003.htm
I just did mine a coupla weekends ago.....I have a million pics but no write-up and they are not on the web anywhere just yet.
FYI I installed Alpine SPX-177R components in the front....SPR-17LP in the rear doors. (all from Ebay) Alpine F240 is HIDDEN in the rear of the truck...I modified the right side "cargo strap holder pocket" and my amp is in there. I need to post pics of this cause it is a sweet setup for those that do not want to have an amp bolted the back of a seat. I will probably get(need) a bigger amp.....this one was leftover from Tacoma days. FYI I aslo used my Head Unit....Alpine CDA 9811 from Taco too. So everything I have is Alpine.....I wanna keep the thieves happy....no need for them to get mixed compoenents right????
I would DEF get an amp......anyone that tells you you don't have to is just trying to get you to buy SOMETHING.....but if you are going to upgrade your speakers they will have much bigger magnets than stock and will need more power(much more)......especially if you get a component set. Don't half do it.......if you're gonna get wet jump in with both feet.
OH.....almost forgot.....your new speakers will NOT fit in the factory door mounts.....I recommend going to Tacotunes.com and buying the UHMW(Ultra High Molecular Weight) plastic mounts from Robert.....they make installation WAY faster(no need to cut wood(plus wood rots, swells, etc.)......these are worth their price....there might be other mounts like this out there but these are the ones I use. Turns out the guy lives in San Antonio with me so I went over to his shop and he helped me remove the door panels and took pics....I think they are planning are marketing the mounts for 4Runners soon.....they already fit though.
Let me know if I can help.