Just to stay on-topic on the off-topic physx.
Discussing PhysX seems on-topic to me, considering the game this thread is about uses PhysX...
If you have a decent spare Nvidia card just sitting around, it's at least worth a shot setting it up as a PhysX accelerator to get the most out of Alice.
You guys might want to read this article and consider if you really want to pay nvidia to get a new gpu: http://semiaccurate.com/2010/07/07/nvidia-purposefully-hobbles-physx-cpu/
That article is known to be sensationalist, and greatly overstates the performance gain you would get by recompiling PhysX for SSE. The article claims a 20% speedup, when in reality it's more like 8% (and only in some circumstances).
Besides that, the version of PhysX that runs in software on your CPU was coded entirely by AGEIA (when this article was written, Nvidia had hardly altered a single line of code), which means optimization issues like using X87 instead of SSE were there before Nvidia even got their hands on it. Since then, they've done some work optimizing the mess they inherited from AGEIA.
More recent versions of PhysX are compiled for SSE, and we have seen an ~8% speedup for it. A decent GPU still ends up being substantially faster than your average quad core CPU due to how parallel GPU architectures are.