I'm running vista w/ 2.0 GHz core 2 duo, 4 Gigs RAM, 8400 nvidia card and the game runs perfect save for when advent bubble ships are in proximity. Then the game slows way down. I havent noticed if my 2 cores are splitting the load or not, but things seem to run smooth even late game with 6 stars and 150+ planets. Only problem I end up with is the game crashing or minidumping. Might try vista or adding more RAM if you have the means. But specifically I've no clue on getting processors to split the difference.
You won't be able to, at least not with most games. It's because of the way threads are handled by the CPU at the most basic level. If multiple cores (or CPUs) are modifying the same data it will enter a deadlock state and pretty much lock up since it can't decide which is valid (do I trust the answer from Core 1 or Core 2?). At the basic level, while most applications are coded in a language that is multi threaded, games take on their own unless they are specifically coded to be multi-threaded games. Having both cores tell your video card to draw something different on the screen at the same time is an issue, just like both cores trying to read/write to the same section of memory, etc. The game needs to be coded in a manner permitting multiple independent threads (for instance: one for graphics, one for I/O, one for AI, etc) and the O/S and CPU will assign threads to cores as it sees fit. An example of this would be Supreme Commander which splits itself in multiple threads (I/O, AI, Video, sound, etc) the operating system will offload the seperate threads onto different cores. They don't have to be different cores for each one though just that the game/programs has to be coded in such a way that the threads that make up the game can be separated from each other and not end up deadlocking the system. One core can handle multiple threads (it's doing it right now for you with multiple programs open) but unless the programs as I've stated is coded to in a multi-core able manner it won't be able to.
I just wanted to add, that this is why having a dual/quad/multi core system isn't a gigantic boon to gamers. Sure, in the future it will be nice when games really support them but right now they really only provide a marginal benefit of moving the background tasks off the same core as the game (which is a bit of performance boost but not "huge"). It is nice when running multiple applications though at the same time since a whole programs can be moved from core to core.
Note: I'm not an professional programmer or anything so the specific of how it's coded I'm not sure of just that at a basic level this is why that occurs.
