Paahtis: I made batch file to enable alt+tab. (found on GOGwiki):

@echo off
set SMACDIR=C:\Games\Sid Meier's Alpha Centauri
sdbinst -u "%SMACDIR%\game.sdb"
sdbinst -u "%SMACDIR%\game_add.sdb"
pause

As said in topic it can't find game.sdb nor game_add.sdb in the Alpha Centauri folder. I searched the folder myself and couldn'd find either file. Has GOG renamed those files or something?

I also tried renaming trick on terran.exe and terranx.exe, but it doesn't work properly.
Is there any other methods to remove alt+tab block?

Goodaltgamer: Did you check this thread?

http://www.gog.com/forum/sid_meier_s_alpha_centauri_/alttab_disabled

Paahtis: Yes that is the thread I found this batch file.

Also when I write DirectDraw=0 to alpha centauri.ini and in game press ctrl+alt+del/alt+tab Windows taskbar comes visible, but I can't open any windows.

Goodaltgamer: Did you also try:

http://www.gog.com/forum/sid_meier_s_alpha_centauri_/alttab_disabled/post27

EDIT EDIT: Problem solved, I copied sdbinst.exe from the system32 folder into the Alpha Centauri folder, I suppose sdbinst only looks for the root file if you do not give it the address.
????

Bonedaddy9: How did you solve this? i transfered sdbinst.exe like you said, but all I get is:
File C:\Windows\AppPatch\Custom\{3565ae7a-df66-4901-94fd-50821b5ffb9b}.sdb is not installed. Uninstalling Halted.
twice, and then Press any key to continue.... which closes the window and does nothing else.