Motors with gearboxes, these are ideal - http://www.argos.co.uk/static/Product/p ... +DRILL.htm

Wheels, I'd advise the robochallenge wheels with the nut insert that screws directly onto the above motors - http://web.me.com/robochallenge/Robo_Ch ... nical.html

You can also find drill motor mounts from the robochallenge guys which will allow you to directly mount the motors to a chassis.

Armour - cheap simple armour that's easy to machine i'd recommend HDPE, http://www.directplasticsonline.co.uk/

Look at using around 8mm plus for some decent hard wearing armour that will take the hits from the majority of robots, spinners included.

Batteries, you could either use the ones that come with the drills (slightly underpowered) or these http://cgi.ebay.co.uk/12v-NiMH-3700mAh- ... 563e83073a

You will need a charger able to charge them.