for diplomacy and trinity (which can play a diplomacy mod) the usual path to the mod folder is
'C:' drive, the Mods NEED to be placed here for xp ( the 'C" is the windows install drive
C:\Documents and Settings\'user name'\Local Settings\Application Data\Ironclad Games\Sins of a Solar Empire\Mods-Diplomacy v1.37
or here for vista/windows 7
C:\Users\'user name'\AppData\Local\Ironclad Games\Sins of a Solar Empire\Mods-Diplomacy v1.37
NOTE the first two folders after the 'user name' are hidden , so to see them you must first click on 'tools' then 'folder options', then 'view', then click on 'show hidden files& folders' then click ok, then you will be able to browse your want to the folder. I suggest when you find the folder that you create a shortcut to it on the desktop
NOTE 2 the 'user name' in the above paths is your WINDOWS login user name, eg Administrator
note 3 these shortcuts assume your windows is installed on 'C' drive
harpo