cjrgreen: No 7600M meets the minimum requirement. The minimum requirement is actually for a 16-ROP graphics card that can push 10Gpixels/sec. The 7600M series is 8-ROP cards that can do 3.6-5.8 Gpixels/sec.
The difference is enough to limit the better 7600M cards like the 7670M or 7690M to medium settings at reduced resolution like 1280x720 or 1366x768, and to make the game sort of unplayable on the low-end cards like the 7630M.
There is also the possibility (with Sony drivers, it's extremely likely) that the computer is trying to run the game on the on-chip Intel graphics, which are much, much worse. Switching to the dedicated graphics under Windows 8 does not even work on many models.
Switching between on-chip and dedicated gfx works on every other game, so that's not the problem. I think it's a really specific problem, because I can run Bioshock: Infinite on all high settings. The Witcher 2 has a bigger world and all, but still I should be able to run it at least on the lowest settings.