Stalker Lost Alpha instal help need please. Thread

Ok guys new at this. I have Stalker SOC from steam. would like to try this lost alpha. could some on tell me what file I need to download and where in the stalker soc I need to install lost alpha. Also have windows 7 home prem 64bit

this is the error I keep getting when I try to start the game.

Expression : FS.exist(fn,"$game_textures$",buf,".ini")
Function : CGameFont::Initialize
File : GameFont.cpp
Line : 75
Description : c:\games\steamgames\steamapps\common\stalker shadow of chernobyl\s.t.a.l.k.e.r. - lost alpha\gamedata\textures\ui\ui_font_hud_01.ini

Ok I have downloaded stalker lost alpha v1.3000 all 4 parts . part one worked just fine , parts 2 , 3 and 4 when I go to unzip them with 7zip says Data error : S.T.A.L.K.E.R._LOST_ALPHA_v1.3000_setup\game-maindir.7z.002

Edited by: xKRULLx