As for cleaning, simply gently brushing with a soft, lint-free cloth (from center to edge, never in a circle, or you might create a scratch that parallels a track), should be enough.
Regarding scratches: If the scratches have penetrated the substrate layer of the actual data, there may be little you can do. There are CD scratch remover products (I'm sure Doug Burnside will chime in and recommend one here) but they are only useful when removing scratches from the clear plastic protective layer.
The best thing about digital audio extraction from CD's is that it's often possible to recover the data from a scratched CD if the audio isn't completely trashed. The error-correction mechanisms in some CD rippers will pull valid data out of places that would otherwise cause a consumer CD player to skip like crazy.
I've got two B-52's albums which have little or no silkscreen ink protecting their top substrate layer, and got scratched badly enough to prevent them from playing in a regular CD player. However, most ripper programs will rip them just fine and make a perfect MP3 out of them.
For more information on ripper software, please consult
the FAQ.