I got 3 modded xbox's, 2 with mod chips and 1 softmodded.
I used to fuck about with them a lot a few years back.
Chimp is the easiest way to softmod long as you got a modded xbox already that you can clone with the program.
Back up your hdd eprom first though as kp said and always use an official controller like neuroticmoose said, very sound advise.
Don't think you can tsop flash 1.6 xbox's so bear that in mind, and the 80 wire ata cable is only used when you're sticking a sata hdd in your xbox.
The standard 40 wire cable causes a bottleneck between the xbox and the sata, and you'll end up with a slower xbox.
With an ide hdd, you will not notice any difference with an 80 wire cable.
Xbox is notoriously picky with sata hdd's as well.
Also remember to get the longest 80 wire ata cable that you can, seriously, it needs to be 24 inch's at least. there's a crazy amount of origami folding involved when fitting the new cable.
EDIT.... sorry guy's it's been a while since i messed with the xbox, chimp is only for cloning an already modded xbox's hdd to a bigger one.
No good for softmodding.. my bad, apologies.