Go to "Setup-bp" in your main S.T.A.L.K.E.R. dir. Chose your language and for Password # 1 input "pseudodog" to unlock the multiplayer map Pool as well as the UK and US military multiplayer skins. For Password # 2 input "snork" to unlock the multiplayer map Dark Valley as well as the French and German military multiplayer skins. These codes are working only on the limited version.