SYMPTOMS:

Civ 4 patched to version Rev C reverts back to Rev A after I install the retail Warlords game.
or
After I install Warlords on my computer, CIv 4 loses certain sounds and Gamespy support.

RESOLUTION:
Solution:
After Warlords is installed on your computer, reinstall the Civ 4 Rev C Patch, and any Warlords patches.

Reason:
The Rev A patch was included in the Warlords retail game. Since then 2 patches have been released. When Warlords is installed it overwrites the CIv 4 app. If this is not done, Gamespy support and certain sounds will not be present in your Civ 4 game.