ICEBIKE has a good page describing studded tires, including how to make your own. The basic process is as you describe: drive screws from the inside of the tire and cover them with something to protect the tube.
- Count the knobs and evenly spread out the 25 screws for each side.
- Punch holes, from the outside of the tire, into the designated knobs.
- Use Robertson bit in the drill to drive the screws in the tire from the inside.
- Put liner inside tire and make sure it covers the screw heads
- Put a generous dusting of baby powder between the liner and the tube.
- Mount tire on the rim (ouch! watch out for the points!)
- Inflate to maximum pressure. Put the wheel on the bike (mind the points). Spin the wheel to make sure that the studs don't catch on anything.
I think the takeaways here are that you don't need screws in every tread block and that the screws shouldn't be in the center. Screws placed in the center of the tread will simply wear down quickly; you really just want them on the outer tread blocks, positioned such that they barely touch the ground when the bike is upright.