I downloaded the gog downloader, but it won't start, even when i check the open box at the end of the installation? am i doing something wrong? is there a virus? is it my firewall? is it that i'm using chrome?
If the downloader gets broken after using it deleting this folder usually helps (may differ depending on the OS you use):
C:\Documents and Settings\USERNAME\Local Settings\Application Data\GOG.com
Since it seems that it didn't work for you to begin with I guess it may be about the .NET framework. You can download it here
. Pick the grey box on the right (which says "Install .NET now").
I didn't get any of that. can i just use a normal downloader?
You can. There is a "GOG.com Downloader mode" switch on the account page. You see it after selecting a game, in the regular shelf view it's on the top right, in list view it's just above the downloads. If you turn it off you can download stuff in a regular manner through your browser.
You can download most games this way just fine, it only tends to become an issue in case of larger games where you will have to manually download several files and may get a corrupted download (which means that you will have to redownload the entire thing unless you try again using the downloader). And with the downloader you can download a single game over many sessions without losing download progress when you turn off your PC, it's a luxury you don't have if you download via browser.