Is there anything special needed in order to install the Construction Set (from my original discs) to the new Steam-version of Morrowind?

I've read that some things are bugged just by virtue of being in the Program Files (x86) directories so .....

Well, I just copy/pasted my CS from my old disc install to my Steam install and it worked perfectly.
As to the PF(x86) issue, I couldn't get my disc install to work at all with Win7 and (x86) so I moved it to its own directory. With Steam, however, I left it in the default path and had no problems.

Try this - http://morrowind.nexusmods.com/mods/42196