Three long shots ...
1. Obviously done lots to try and fix it. So its worth doing a TOTAL purgeof Civ IV - gets rid of old bits that may be around causing clashes
http://forums.civfanatics.com/showthread.php?t=152620
2. Once thats done, reduce the pagefile - its large at 326MB, there could be a background program clashing - need to reduce anyway, that background stuff pinches resource availability
Background Applications & Services
Start Button - Click - select Run - type "msconfig" no quotes - press enter
Click Service tab - tick the box "Hide all Microsoft Services"
tick the box "Hide all Microsoft Services" is very important - you MUST have this ticked to avoid stopping essential operating system services - it MUST be ticked (not empty)
Press disable all
Click the startup tab
Click disable all
Go back to Services Tab - double check the "hide all Microsoft Services" Box is ticked and not empty
Click ok at the bottom of the screen
Reboot
When it settles after boot, run the game.
If it works, bingo, a background appis clashing, restart them one by one to find out which one etc
3. Driver purge. As with system install, you can leave bits of driver around when loading new ones. If you go to the ATI site - then page for latest XP drivers you will see reference to a driver cleaner. Download that, purge the beast, on boot up refuse to allow windows to load drivers, you end up with a horriblelooking screen 640x480 low texture.
Then could try Omega drivers, have a good rep
http://www.omegadrivers.net/
Click ATI Radeon - Click sub menu Archive - Click sub menu Win 2K - try the 5.11
That way you are guaranteed you have an absolutely clean installation, and no bits from previous 3am attempts laying around tocause issues.
Of course, may not work for you ... you may have done it already ... but this 'cleaning' exercise has worked for many who had old bits laying around causing issues.
Regards
Zy