I had this problem also when i upgraded from SnowLepard to Lion and Mountain Lion. What you need to do is take a old snowlepard disk and install Rosetta on your machine that's running the new operating system. Once you install, you should be fine. If worse comes to worse and you cant launch it from the cds, make DMG's in disk utility and go about installing it that way.FWIW, I am still using Final Cut Pro 6 (from Final Cut Studio 2) on my 2013 MBA under 10.8 and it works fine. However there is one "gotcha". The FCS 2 installer is not a universal application and requires Rosetta. Since Rosetta was dropped in MacOSX 10.7, you will not be able to install FCS 2 on anything newer than MacOSX 10.6.
If you already have a working copy of FCS 2 installed on an old machine, the migration assistant will move it to the newer versions of MacOSX. But if you use the original install install disks, they will not run since Rosetta isn't present.
I have not, as yet, attempted to recreate HawaiianHippie's success.Apple has created a "bug" in the attempt to install FCP6 in Lion, Mt. Lion and Mavericks, which makes it look like Rosetta is needed for a PowerPC app, the installer, so as to make it difficult for the use of FCP6 in these versions of OS X!
HawaiianHippie has discovered the best and safest possible solution to this problem:
I have now successfully done this on four computers, brand new iMacs running 10.9.4. And I've discovered an even easier way to do this! You don't need to edit the plist file, just move it into the Trash. Install proceeds normally. You can return it after you're done if you like, I don't know what (if any) possible repercussions might come from leaving it deleted.
The file, as indicated on Jeremy Johnstone's blog, is
(Note that when you get to Installer.app, you will have to Control+click and select "Show Package Contents")