For the others,
1) Dl the Core Update from
Graviteam
2) Install the Core Update (I just install it in my game folder)
3) DL your .exe from Gamersgate (the Game updater should create one folder called "GamersGate temporary files" with one sub folder for each add-on)
4) Launch the game and select "Update" in the menu
5) In the new windows (Game updater) : select each file "desc.addpack" (one per add-on)
6) Select "Save and play" on the game updater
Sorry for my English (i'm a French player)