On Windows 7 Pro, Blackwell Bundle runs fine but Broken Sword fails with message 'missing or broken openGL drivers'.
Trying to update/install these drivers is, after much trying, beyond me.
Any suggestions ?

If you're using a laptop and/or an onboard video chip it's possible it doesn't support certain OpenGL versions.
I believe that causes the same error.

I feel the question should be made, have you contacted support? They should help you out with this kind of stuff as part of the refund policy, at the very least.

What is your graphic card ? Radeon ? Which Broken Sword is it, the 5th ? There was a problem with the exe. file of BS5 on some versions.

Do you use the graphic drivers that Microsoft delivers through Windows Update?

As far as I know these don't support OpenGL. You need to install the drivers from the manufacturer of the chipset on your graphic card. Most likely you will either have a NVidia Geforce or an AMD Radeon card. If you have an old laptop or notebook you might also have an Intel chipset. You need to find out what hardware you have in your computer, download the correct drivers and install them. That's pretty straightforward and not too difficult.