An Nvidia 9600 isn't a bad card. It's not as good as a GTX 260, but it should be good enough for any adventure games.
You don't say whether you have XP, Vista, or Win7.
This site shows where to go to enable or disable hardware (graphics) acceleration in XP.
http://support.plato.com/kb/concept.asp?id=4689For Vista and Win7, it's probably easiest to do it through dxdiag
(Start button --> Type the word
dxdiag
into the Search --> Display tab --> adjust slidebar and save.)
If your acceleration looks OK, you may have a problem with your drivers or your video card may be developing problems. If you think the card itself is the problem, try reseating it first -- unless you just want to go ahead and upgrade it.