I ran into the same thing months ago, tech support sent me a form letter. I yearn to plat the bg series from the begining again, and to try tdsotsc but alas, I have found no recourse. I bought another copy of the game from another retailer for posterity, it wouldnt install either.
if you come to a solution please let me know, either in this forum, or via my email that is in my profile.
good luck