Thanks for response,
This poses some more questions though.
1. What’s the best way to install BCC4 for MC3 on OSX 10.5? Running the BCC 5 install disk that came with MC3 doesn’t give option to install BCC4. 
2. Is it possible to do a clean uninstall of BCC4 afterwards? I dont really want the extra folders and doubling up of effects in the effects palette etc.
Cheers,
Todd