Up to you... depends on the rating of the fets or power transistors.

You could just hook up the servo wires to one of these instead of the fets or power transistors.

http://www.jaycarelectronics.co.uk/prod ... ?ID=SY4086

Cool. We have a huge stack of dead drills in the workshop at the moment so I'll raid them for MOSFET's and resistors, see what I can find.
..you'll need to find / buy the resistors as the drills don't have them.