Do you have any problem with the game installation?
Be sure you have upgraded your Homeworld 2 to version 1.1
clear your ...\Homeworld2\Data directory from any other installed mod/addon, your ..\Homeworld2\Data directory must contain only files/directories listed below:
install Complex in your Homeworld 2 installation folder;
run Complex on your desktop.
If you have Complex in the big format,
copy the file Complex9x.big in your ...\Homeworld2\data installation directory (example C:\Program Files\Sierra\Homeworld2\data\Complex9x.big);
open your shortcut to Homeworld 2 (in your desktop or whatever you have it) and type -mod Complex9x.big at the end of the path (ex. "C:\Program Files\Sierra\Homeworld2\Bin\Release\Homeworld2.exe" -mod Complex9x.big);
note the case sensitive and space sensitive nature of this command line.
If you still have problems, try to post on the Complex forum