Installing both 64- and 32-bit versions

I have just purchased Technical Suite X6 and am very impressed with the 64-bit speed, but have discovered (like many others) that my scanner's twain driver will not talk to the 64-bit version.  I have tried to install the 32-bit version as well, following instructions to launch the 32-bit install from the DVD, but it pops up with the following message:

"The installation was not completed.  To complete installation at another time, please run the setup again.

You cannot install this product because it is already installed.  To change your installation from 32-bit or 64-bit, you must first uninstall the existing version.

Click finish to quit the setup".

So, is this a limitation of the education edition?  This is not an upgrade edition and I still have Designer technical suite x5 installed (different licence).  An before anyone asks, I only have the 64-bit version currently installed.
OS: Win 7 64-bit.

Any other suggestions?
cheers
Bill