Game locks up after 3-4 hrs

I just bought SMAC last week. I am new to PC games but not PC's. I am
running 1ghz Celeron with 256m ram and an 80g HDD. XP(home) operating
system.
1 gig Celeron with 256m Ram, 80 gig HDD.
I installed whole game to my HDD and also patched Firaxis fix for
windows XP.
I have only played a few times (single player) and after a 3 or 4 hour
investment of my time, (Not to mention I was winning), it just locks
up, I can still hear the background music really low but it never
started working again even after a several hour wait. 
Cntl/alt/delete sowed it was still running vs not responding.
I thought maybe I just had too many units running in automatic mode or
something.
Any advice or explanation would be very welcome.
Thanks