@reimiux
it appears i was giving wrong information... (my method is outdated, worked before the temp\downlaoding folders stuff)
i did this method with another game and it works wonderfully:
unninstall gta in the steam games list.
copy the "cracked" version into the steamapps\common folder (in my case: C:\Program Files (x86)\Steam\steamapps\common)
click to install the game, the window to install will appear, make sure the directory is correct (in my case is C:\Program Files (x86)\Steam)
the steam client will start a process of discovering the files. if you putted it in the right place with right names, it will do it's job and find the games.
the cracked files will be marked as "corrupted" and the steam client will re-downloading theese "missing files"