Media 100 i V7.5 is OS9 only. Media 100 V8 was the first version that ran under OSX. If you only have a encryption code for Media 100 V7.5 you cannot run it on OSX, you need to run it on OS9. There is no way to use V7.5 in classic, since classic applications cannot access their hardware under OSX.
Time to leave this version in the past (actually it was time to leave it in the last 5 years ago, now it really time). I mean, it's been 7 or 8 years now. So, time to upgrade, we have many new products to sell you that can improve your editing and make the transition from 7.5 to 12 go pretty smooth. Version 12 is so superior in functionality to 7.5 I don't even know where to start.