Well, your post was several months ago, so maybe you don't care any more, but I managed to install and run it after some trials. First, to install it, I had to right-click on the setup.exe (or whatever the program name was; i don't have it in front of me) on the CD and right-click and choose propertied. In the Compatibility tab, I picked "Windows XP (Service Pack 2)".
After it installs, go to C:\Program Files\3DO\Heroes 3 Complete.
Do the same thing (Windows XP SP2 Compatiblity) for ALL executables in that folder. There are a bunch of them. If you don't do it for all of them, the program will crash occasionally.