I am not a computer expert. But I do enjoy tinkering.
I was experiencing a few problems running DA on a laptop. The laptop's Nvidia 7800GTX (256 meg) card, 2 gigs of memory, and 2.26 ghz PentiumM process are not that old (yet).
The first thing I did was update the video driver. I ended up purchasing driver cleaner pro for $10, but Kryo wrote there was a freebie version of software floating around. After reading the driver cleaner pro instructions (which are VERY detailed) and running the software, I loaded up a slightly older version of nvidia drivers for my slightly old video card.
I still experienced crashes every few turns while playing on gigantic map with abundant everything, 9 races, and 8 minor races. So, I turned to CachemanXP from www.download.com (otherwise known as C/NET). I cannot use the auto-optimize button since I am using the shareware version, but I set "File Cache Management" to "CachemanXP controlled." I left everything else alone. I loaded up DA, the alt-tabbed out to CachemanXP and set the "Priority" for DA to "HIGH."
I played for hours last night on gigantic with abundant everything with no problems what so ever. This did the trick for me, so I hope it helps someone else.