I second waltr's warning about the motors you linked to. The only way they will power a vehicle with a wheel directly attached to it is if the vehicle is going down a steep incline. Those motors will not be able to power a robot
with wheels directly attached to them.
I purchased several of these motor/wheel combos from MPJA
. They didn't work at all. Without a gearbox, the motors couldn't move their own weight.
You'll need one of SparkFun's (or other vendor's) motor with a gearbox in order to power a robot or other ground vehicle.
There are a variety of ways to mount wheels to gear motor axles not originally intended for each other.
Here's an example of mounting Vex Mecanum wheels to Rover 5 axles
(post #29 of thread).
Pololu and other robot supply places sell mounting hubs
for a variety of axle sizes to make it easier to mount wheels.