If they are really *very* light you can first try a regular polish with your PC, but don't expect a miracle, glass is very hard to polish out. If it is more of a slight marring than a scratch you might have a better chance.
If that doesn't "cut it" (pun intended), then
Eastwood and JC Whitney both sell a kit for polishing glass. The following thread contains some info from a member (JohnZ3MC) that used the JC Whitney kit with good results:
http://autopia.org/forum/showthread.php?t=78939
I have not personally used one of those kits to remove a scratch, but Eastwood typically sells pretty good stuff. I would be very careful and follow the instructions, you sure don't want to bugger up your windshield worse than it is now.
BTW, what were you scraping it with?