Like the others have said, polishing the glass will work if the scratches aren't too deep (same as with paint). The glass polishing kits are available online. If you have access to a random orbital polisher (such as a Porter Cable 7336), I would use it over a drill. With a drill (or orbital polisher that just spins in circles), you can distort the glass. Not a good thing for a surface that is supposed to be distortion-free for optimal visibility.
When talking about a random orbital polisher for actual polishing work, the electric "buffer" types from Walmart typically won't cut it. They just don't have the power to do any serious defect removal. You can really put some pressure on a PC without bogging it down, and the random orbital action help ensure that even improper technique won't destroy the surface like with an actual rotary.
If you have to use a drill, I'd suggest keeping it moving to prevent polishing too much in one spot and distorting the glass. Slow but continuous movement will pay off here. Along with a lot of patience. Glass is harder than paint, so some effort will be required.
Have you checked with your insurance company to see if they will pay for new glass? I had mine replaced with the insurance company paying for it because of many specks and scratches. They have paid for several repairs from rock chips, too. According to my agent, they're more than happy to pay a little for a windshield compared to the cost for the entire vehicle because of a crash resulting from poor visibility. Your insurance company/coverage may vary.
Dave
