Sufyan: Your soundcard looks like a weak link. Try playing a heavy section of the game with sound disabled (if possible) or lower sample quality. Drivers, drivers, drivers. See if there are unofficial ones or beta drivers to try. Also, have a look at your mouse drivers. Odd suggestion but I have had performance issues in another game a few years ago.
Lastly, you may be looking for a bad combination of settings rather than just one or two that tips the scale.
SnowGabe: Can sound cards really affect performance?
I think I've updated all of my drivers.
Most sound cards are garbage and yours don't even seem to be a physical sound card but some integrated chipset. Further more, many games have really poor sound engines that are way more processor heavy than you'd think necessary. It is a forgotten field in game development and in fact hardware/driver development. Calculating and processing sound effects is a large chunk of the equation so if no graphics tweaking seems to affect performance, start experimenting with sound settings.
Lowering the amount of audio channels, lower sample quality, testing different hardware acceleration settings, lots of things can drastically affect performance. This is a nightmare, it is like game developers do not give a crap and just dump third party stuff in there hoping it will work. The sound card market is not as focused and clean as the graphics card market, and it will show once you start looking closer. Creative Labs has pretty much been the one successful company when it comes to consumer sound cards and they squandered their monopoly over the years like they just don't care.
