The patches can be unpacked with WinRAR, but this won't help you since you still won't be able to install it. The patch shouldn't be saved in your override folder, although I doubt it will do any harm there it is still best to save it somewhere else. It doesn't actually matter where you save the patches since they search the registry to find the game. Evidently the patch's installer isn't finding the game in the registry. So...
- If you have Tales of the Sword Coast installed you only need the TotSC patch (version 1.3.5512) you do not need the straight BG patch as well.
- Are you using the right language patch? For BG1 there are separate US and UK versions for BG2 there is just the english version. (I haven't looked into patches for other language versions).
- Gah... I'm out of ideas for now.