Legally you will need another licence but that's no different to a dual boot.
I shouldn't need another license... the old program is bought and paid for, and at present is not installed on any computer that I own.
Perhaps the compatibility mode options might work
Nope. Been there, done that. The installer won't do the installation, quits with a "InstallShield 1628 Failed to complete installation" error.
Oddly enough, the very first time I tried to install the program on the new computer, it
did install and sort of run. The display was all strange, showed everything in wireframe instead of rendered, so I figured the install was corrupt, deleted the installation and re-installed. Except it never, ever would reinstall again.
The program vendor has said that it won't work in Windows 8.
The learning curve for the old program was horrible, and the new version is enough different I'd have to start all over again. I'd prefer to stay with the old one if I can.
tanstaafl.