Bob -
You will want to use a thicker polystyrene sheet than the most thin plastic in order to use as a counter. John may know the exact thickness to buy. The plastic is much better than standard cardboard wargame counters.
Best to go to like a Staples and buy standard 8.5x11 printing paper with an adhesive back. You can print out a counter sheet, peel off the adhesive backing and paste it right to the plastic styrene sheets. You'll want to minimize the margins as much as you can (maybe .5 inch on all sides I think is the smallest you can go) and then when you print size the page to fit to one page.
Then best to score the plastic sheets with an exacto knife or a scoring wheel and snap the counters apart.
When I first made counters for the game I just used the Microsoft paint program. The resolution is not very good, but good enough. I never bought Photoshop, but there are free online downloadable programs that allow you to make high quality counters. I downloaded and used PhotoFiltre 7 to make good quality counters. It is not as simple as paint, but I don't think as complicated as photoshop - and it's free.