I'm trying to install the CS and this is the error I'm getting when I launch the exe:

Unhandled exception
Error Number: 0x80040706
Description: Object Reference not set

I got the file from here: http://cs.elderscrolls.com/index.php/The_Elder_Scrolls_Construction_Set

Is there anything I can do? I'm using windows 7 and I tried running it as administrator but I get the same error.

I think this needs to be installed away from anything the UAC knows about. So, create a new directory on the root and put it in there.

In fact, you should put Morrowind in the same folder, so the game is one sub folder, the editor is in another. Name the directory like this:

C:Games/Bethesda Softworks/Morrowind
C:Games/Bethesda Softworks/Construction Set

I think it wants to be called Construction Set...

Edit, the cool thing is, you can just move the existing game install, well, just move the Morrowind Folder to the Bethesda.... folder, you don't have to reinstall it!!