assuming you have sins 1.16,  the mods NEED to be placed here for xp
C:\Documents and Settings\'user name'\Local Settings\Application Data\Ironclad Games\Sins of a Solar Empire\Mods-v1.16

for entrenchment 1.02 the mods go here
C:\Documents and Settings\'user name'\Local Settings\Application Data\Ironclad Games\Sins of a Solar Empire\Mods-Entrenchment v1.02

or here for vista/windows 7 sins 1.16
C:\Users\'user name'\AppData\Local\Ironclad Games\Sins of a Solar Empire\Mods-v1.16

for vista/windows 7 entrenchment 1.02
C:\Users\'user name'\AppData\Local\Ironclad Games\Sins of a Solar Empire\Mods-Entrenchment v1.02

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

hope this helps

harpo