If the DVD is physically damaged, the chances are small that the
read-surface can be re-finished. For example, some major PC stores do sell
scratch removing kits.
If the DVD is physically OK, then a progam called ISOBUSTER can probably
read it and recover files. ISOBUSTER is part free ad part shareware.
Basically, install the program and see whether it can help. If you want to
try the advanced options, mostly related to creating/modifying ISO file,
then you will have to buy a licensing. Read the help carefully, as
ISOBUSTER has several way it can try to read a DVD, and some may work when
others fail. For example, it can bypass the XP reading routines, and that
solved one of the problems I had.
http://www.isobuster.com/