I've tried using both the GoG Downloader and directly downloading the game through the browser three times each.

During the installation of the game (6 times now), I get an error message stating that the file xp3.bif is corrupt.

Is there a solution?

I'm not sure...but have you tried the 1.69 patch?

(sometimes refered to as the "critical rebuild"...)

I don't know anything about a patch. All I did was download the three files that were presented to me through the GoG Downloader and using the direct download through the browser.

Where do I go to find this patch file?

Patch is not needed, GOG version is already up to 1.69.

Does this error happen during or after integrity check? If the check is passed, the files themselves are fine.

If you have an AV program running, try disabling it for the installation. Also make sure you're running the installer with admin rights (right-click on .exe, pick 'run as administrator')

If integrity fails, try disabling firewall for the time of downloading.

All integrity checks are passing. I disabled my AV for another attempted install just now and got the same xp3.bif corruption error.

Get the 1.69 patch from here:

http://www.neverwinternights.info/players.htm

Won't cost you much to try it at least...

Double check that your AV is disabled. There have been a number of posts from users, such as this one, who find the install problems persist because the AV is still active.