So recently, I've gotten civ IV working after an HDD clearout, I had a baffling (yet successful) evening with it. My PC is comfortably within the specs for the game, but due to age and wear and tear from use, I run the game on lower graphical settings. I have a penchant for playing on 'huge' maps. Anyway, it started seizing up on me again, freezing for 30 seconds very regularly, occasionally crashing. A quick google turned up a tip saying to try the game in windowed mode as opposed to full screen. I did so, and it completely fixed the problem.

Now comes the weird bit. In windowed mode, the resolution setting I was using rendered text illegible, so I tried a few different ones, eventually finding the biggest resolution to work best. However some text was still a bit sketchy, and I was annoyed by not being able to bump my viewpoint about with the mouse, so I gave fullscreen another go... And it works perfectly! My question is, surely a lower res should be less demanding on the PC (although not by much), how does a higher res not only work better, but make such a dramatic difference to how the game runs?

Please be gentle, as I'm not hugely computer literate, I know enough to get by, but that's about it. Cheers giys!

To test if it's not something else, you could go back to the low rez and see if it starts crashing again. Maybe a particular resolution is "optimal" for your hardware or system settings, but it is hard to be sure.