Do i have to download part 3 first? it dosnt work or do i have to move or use installer 2 first from my downloads?

I am not exactly sure what your question is, but each game is a stand alone installer. You can download fallout 1, install then play it without downloading and installing Fallout 2 and visa versa. Same goes with tactics. Please correct me if I'm not understanding you.

I'm guessing you're asking about Fallout Tactics since it is a much larger download than the other two games. As with all multi-part downloads, you need to download all parts into the same directory and launch part 1 which is the installer itself (part 2 and 3 etc is the data). In this case it is called "setup_fallout_tactics_2.0.0.8.exe".

Didn't think about the multi-part thing. I guess the GOG downloader has spoiled me. :D