How much video ram? How much computer ram? Crappy hard drives? Other things can lead to this...even maybe the 4.5 drivers you are using.
9700 pros have 128mb ram, my system has 1 gig ram and a SATA 8mb WD 120gig drive (almost half full, fully defragged). The slow down is just enough to be noticeable at points, the worst I've seen so far is the torch-carrying guard in the weapons room in the first mission. The mouselag trick did help, thanks whoever mentioned it.
I've gone back to Cat 4.4, video corruption is much improved, not totally absent though. I can't say the game looks nice
, but it's certainly not bad. The bumpmapping works well at times. Yes we could have gotten (much) better graphics, but I'm not going to complain. The game is still great without it.
As far as sound goes, I've never met a game that sounds perfect with EAX enabled. I refuse to spend money on any more Creative products until they clean up their act (Yeah, I was burned by them with my Aureal 2 card). I'm now using a 5.1 system w/onboard sound, and while it would be nice for sounds to muffle and echo, it's not bad without it. It's great that I get proper surround sound, the Dark engine only supported stereo.