DISCLAIMER: I never have, nor ever will be mistaken for a handyman or professional installer.
That being said, like others, I was afraid to let installers not familiar with the fortwo touch my car, BUT I desperately wanted to upgrade my stock radio sound.
So with the help and ideas of this site and its members as well as a bit of bravery on my part, I embarked on installing my own sound upgrade.
Stock radio was to stay in since I listen mostly to my satellite radio and iPod, so I didn't have to deal with upgrading the head unit.
For the speakers (the hardest part since you have to disassemble the door panel):
http://www.crutchfield.com/S-kfXuUKj...ailed_info#Tab
For the amp:
http://www.crutchfield.com/S-YDx08VL...ailed_info#Tab
And, for the sub:
http://www.crutchfield.com/S-mZvu3Rs...ailed_info#Tab
Yes, I could've saved a few bucks by purchasing these items elsewhere, but the price premium paid off when I needed Crutchfield support to walk me thorough some of my questions late at night.
The difficult part was taking off (and not breaking) the door panel and getting over the horror of taking a knife (to carve a space the for speakers) and a drill (for the components) to the car.
Getting past that, everything else went well - splicing and tapping into wires here and there and then testing the system.
The amp is behind the driver and sub is behind the passenger. The driver seats goes back and reclines all the way without a problem. And while the passenger seat reclines like normal, I did lose about 0.5 inches in pushing the seat all the way back due to the size of the subwoofer.
All of the wires traveling from the back to the front were stuffed underneath the rug along the side of the car. I know I could've done a better job of concealing the amp and sub wires behind the seats, but since nobody would ever see them, that task could be saved for a rainy day.
The result? A 10,000% improvement in sound. The components make a HUGE difference and the subwoofer is just right (and adjustable) for the size of the car.
So far, it's been a week and the car has not blown up yet, so I consider my installation a success.
In all, it took me (remember, I am a nervous rookie at this) 12 hours (on and off) to complete everything with most of it to study and remove and reassemble the door panels.
Moral of the story: If an idiot like me can do this (my college degree is in accounting, not engineering), anybody can.
If any other rookies need some help, I'd me more than happy to help. Or if any pros out there have any advice, let me know - as long as it does not involve the speakers because I am NOT going to take those door panels off again!
In the meantime, the finished (or so) result: