I second the Griot's recommendation. I've polished the windshields annually on my cars for several years now using the Griot's glass polish and their random orbital buffer. It takes me less than 30 minutes and the results are amazing each time. And, if you're in an area that gets a fair amount of rain, your wipers will work so well after you polish the windshield that you'll wonder why you never did it before! I'm not sure if polishing will take care of light surface scratches in the glass, but it wouldn't hurt to try. Griot's offers two grades of glass polish,
fine and
regular. For purposes of removing a light scratch, I think the latter is probably better suited.