There are a couple of unknowns in the equation for torque needed for your application. Screw pitch and efficiency.
But anyway, for example-
screw pitch = 2mm = 2x10-3
efficiency = 70%
mass of platform = 10kg (i like metric
work in x efficiency = work out
torque x 2pi x efficiency = mass of platform x acceleration due to gravity x screw pitch
torque x 2pi x 0.7= 10 x 9.8 x 2x10-3
torque = (98 x 10-3
) / (pi x 0.7) = 0.044unipolar and bip6Nm = 4.46Ncm
The driver you want to choose depends on 2 things - unipolar or bipolar motor? and how much are you willing to pay?
unipolar motors have 5,6 or 8 leads and require a different driver to a bipolar which have 4 leads.
If you wanna keep costs down, then you can build your own driver - http://aaroncake.net/circuits/stepper.asp
otherwise there are plenty of commercial drivers out there to suit your needs.