I'm using a Pentium II, 266 MHz, 64M RAM; and swap space on hard drive set to 128M. I think the longest AI turns I've seen have been 1 to 2 minutes, max; and that was when each AI had 100 - 250 ships (I set the limit to 2000). But it hasn't locked up yet. Of course, I also only play a couple hours at a time. I also only use the standard 1.30, no mods (well, except for adding a few production bonuses for high populations, but those only apply to populations above 10B, which doesn't happen often
). I'm also using a 255 system galaxy; CD Music turned off; max AI's, and max neutrals.