Well, Civ 4 won't run too well on that, but if it really is Civ 3 that you're after, it should be more or less fine. If you can find a cheap-o vid card that would help a lot (even just a $50 or less card would be good...).
civ 3 will run fine on it, i think i ran civ 3 on an old ass p3 with a like 4mb vid card and 128mb of ram. it was a long time ago, one day i came home and my mom had taken a hammer to the computer... funniest thing ive ever seen.
I don't think many realized that it was a laptop . It helps to come right out and say so. I realize that the mere mention of the T2300 should suffice. But still it does not hurt to mention "laptop".
Anyway forget the graphics card comments. Your not getting anything better put into what you have.