stepper motor vs servo motor (and other assorted oddities)

I've been thinking alot recently about creating my own CNC mill
(multipurpose is the plan). I've got some ideas about the mechanical
construction (although some links to ideas concerning ways to make a large
chassis stiffer would be appreciated), however I'm at a loss as to what kind
of drive system to use. I would like direct coupling of the motor to a
ground ball screw (which in turn drives each axis etc), however I don't know
what kind of motor I should be looking for. I'd like for the finished mill
to be highly versatile. Anything from a very high resolution
(repeatability) 1mil PCB design (10cmx10cm), up to an IC (Internal
Combustion) type cylinder bore (with the same level of precision would be
super nice). I realise that this is asking for everything, ie power (to
tool metal, aluminium) and also speed and accuracy for the PCB milling,
however any pointers would be greatly appreciated, I haven't been able to
find much at all on Servo motors.

Thanks,
Bevan Weiss