You'll have to run it in Rosetta. Do you know how to do that?
Thanks for the reply. No, I don't even know what Rosetta is.
Rosetta is an emulation environment that allows software to run on Intel processors (like your computer has) if the software was written for PowerPC processor (like After Effects 6 was written for).
So, you can probably run After Effects 6 in Rosetta on your computer. But the emulation software introduces a lot of overhead. The performance may be painful---i.e., slow.
After you install AE get the info on the application by control clicking on the AE6 icon in the finder. You'll see a check box in the info palette that says something like run in Rosetta. Check that and launch the app.
If this is a clean install you won't have any of the updates for AE6 on your machine so there may be other issues. You can check for updates under the support menu right here. Just search for After Effects. You'll find them here. I don't remember if the 6.5 update was free or paid.