Have you performed Steps 1 and 2 here:
http://hof.civfanatics.net/civ4/mod.php?show=vista
Personally, I don't like designating a mod in my INI like that, cause I run other things. If you plan to only use BUFFY to play the game though, that is fine.
Another option is just create a shortcut from the base .exe and add to the end of the target line of the shortcut..after a space:
mod="BUFFY-3.19.005"
(Note: For some reason - and I use steam version too - I need to add an extra character before BUFFY in the quotes in order for it to recognize the mod. So like :
mod="BBUFFY-3.19.005") No clue if that is just me.
With the shortcut enabled, you can just it to load BUFFY when you want to use it.