
the windows registry is there to register all programs - so it is large - and it is not really intended for manual changes, but:
click on the + sign next to
HKEY_LOCAL_MACHINE
then on the + sign next to
SOFTWARE
then on the + sign next to
Firaxis Games
this should then list
Sid Meier's Civilization 4 Gold
click on the + sign next to it and among others it should list
1.72
right click on that and click on rename then rename it to 1.74
also right click on
Sid Meier's Civilization 4 Gold
and chose rename and rename it to
Sid Meier's Civilization 4
this should allow you to install BtS:
Note: DO NOT do so without setting a system restore point first - any error in manual regedits can cause your operating system to cease booting!