Computer gamers spend a lot of time playing.

The problem is that the AI takes an incredibly long time to make its moves. On day 3, it takes about a minute and a half for each AI turn (4 AI opponents, a relatively small map), even though I've set their speed to maximum. I've tried setting the graphics settings to both the lowest and highest levels, but it makes no difference.
The game is a licensed copy, and my computer has an Athlon 2.8 processor and 1.5 GB of RAM. What could be causing this, and is there a way to fix it?