Advice needed: powering an arduino/motorshield

[MrGlass]

So, I bought an arduino at HOPE. Before this i have had little to no success with electronics projects, but i seem to be getting somewhere by taking the slow and steady process. I put together a motor shield last week, and after some rather ugly hacks managed to get a motor spinning to my great enjoyment. I'm now taking apart all sorts of old spare electronics (including barely used robotics kits) to gather parts before moving on to a semi real project.

I need a reliable way to power my setup, but i have very little engineering/electrical knowledge (I'm a CS student). My current setup is as follows:

Arduino Diecimila
Adafruit Motorshield
Various motors and LEDs stolen from anything i can lay my hands on

I'm thinking of getting a wired setup for development as well as a battery, as it seems that battery based setups have a lot of drain. I actually have a pretty good battery pack from my vex kit (7.2v 200mAh NiCd) which i think i can just plug straight into the arduino. As for powered, I don't think I have anything that applies.

So, whats the best way to power a simple arduino based robot? Will my old vex battery work? I want to try to find everything locally, but I live in Manhattan so I'm not really limited by my local crappy radioshack.

P.S. In case my scavenging didnt make it obvious, price is definitely a factor.

[mtbf0]

should be good. 7.2v will give you adequate headroom for the regulator on the arduino, and provide juice for some small motors. keep in mind that all the vex motors are controlled like servos.

any wall wart greater than 7 and less than 30vdc with a center positive barrel connector that fits will work. with higher supply voltages you should probably heat sink the regulator on the arduino if you're pulling much current through it.

[MrGlass]

Thanks. I'm actually using a random motor I found elsewhere for now (a broken battery powered BB gun, actually), though i might switch to the vex ones soon so i can use all the gears it came with.

When i was searching around last night i saw a post that said its better to power the arduino and shield separately. is that true in my case, or just for big motors?

Also, is there some guide to how switches and other sensors work? so far I've just been taking stuff apart and figuring it out with my multimeter, but i don't want to strip open the vex parts.