I've noticed that after copying game files the installer runs some programs. One of them is obviously the ddraw fix, the other is some sort of fixpack type utility. The question is - is this THE IWD Fixpack? What version? Which fixes is it running (all of them)? Is the tweakpack running as well?
Will running a newer fix/tweakpack over this corrupt the game files?

From what I understand IWD Tweakpack and IWD Fixpack from Gibberlings http://www.gibberlings3.net/iwd_fixpack/ were made after all official patches were included GOG IWD and IWD2 were only patched from official patches.

However I'm unsure what GOG.com did to their versions though other than remove DRM restrictions that may cause issues with IWDfixpack and Tweakpack.

I also need help installing IWD mods but Gibberlings site seems to be down and I cant download anything. :-(

I don't know what fixpack it's running, but I can confirm that running the fixpack from gibberlings does not corrupt the game. Not using the tweakpack so I can't vouch for that.

Well, it turns out only the ddraw fix SHOULD be run. However, I had fixpacks left from the previous installation and the installer somehow ran them as well.
I think.