Alright, this got a little more interesting.  I tried running 
BG1 and got an error before the game even started, even before the Black Isle video plays.  So, I figured it was a corrupted 
BG1 installation.  I uninstalled 
BG1 and installed a fresh copy.  I then tested it by making a character and starting up a game, which worked just fine.  With 
BG1 working, I then restarted the 
BWP installation into a fresh 
BG2 install folder.  I noticed after the 
BGT section that there was still no BG1ARE.bif file in the data directory, but I figured I would let it finish just in case.  After the entire thing finished, I tested 
BG2 and encountered the same problem as before.  Now, here's the interesting part: I then went and checked 
BG1 and it is now corrupted and will not start, just like I found it after my first installation attempt.
My initial thought was that this has something to do with the fact that I'm installing 
BG1 on D: when the default is C:.  However, I gave the 
BWP install the proper folder address.  Plus, the 
BWP install process clearly corrupted the 
BG1 installation, so it must have found the thing.  This is the error I now get when trying to start up 
BG1:
An Assertion failed in D:\Dev\chitin\ChDimm.cpp at line number 581
Programmer says: Unable to Open BIF:data\SFXSound.bif
For the record, 
BG1 is installed at: D:\Program Files\Black Isle\Baldur's Gate
Any ideas what's going on here?