Assume that all the use of words in English that I write, here, are in Dutch. That will save time.
1) Do a backup of your registry, under another fillename. This is vital.
2) Click the Run button. Type REGEDIT.
3) Under Edit, click Find, and type in Baldur. Then click for "Find Next." (The idiots who decided you needed a separate control for finding the next instance of a phrase should be demoted to janitor.) Do the same throughout your registry. At each instance, delete the key.
4) Repeat with BG.
5) If you have no other Black Isle Studios or Interplay titles on your computer, try searching on those, too, and remove.
6) Reboot.
7) Try reinstalling. If you've messed up anything else, you can always reload the registry file you saved before starting this.