I used the gog.com downloader to download this game. When the download finished i was unable to do anything, just stare at "download complete". Tried downloading manually and i kept getting an error message when trying to install. Am i missing something obvious? Any help is very much appreciated.

Maybe the download became corrupted on the download process, it has happened to me when I lose connection while it's downloading. Try to re-download and if you have more problems try to contact support.

It's usually a good idea to specify the game you're having problems with, and the error message you're getting.

For example, there may be problems using the downloader with BG2, because it can misname the executable file - in this case it's easiest to download the setup.exe manually (it's usually only 2mb)

Otherwise you can check the support pages for BG1 or BG2 for possible solutions.