Final Cut Studio 2 / Mountain Lion

>Can I just buy an upgrade to FCP version 7?

Sure. But the only place you'll find it is eBay, and things are cutthroat there (not cheap) because Apple discontinued FCP 7.

>Or will I run into the same problem?

The installer for FCP 7 is Intel. It's the installer for FCP 5.1 and 6 that's PowerPC. And while there was a hack on Lion, not so on Mountain Lion.

>I figure that since I am buying the upgrade, I may not have to even install FCP 6...as long as I have the Serial.

Correct.

>I also understand that Apple only supports FCPX on Mountain Lion, but from what I understand, the issues seem to be just installing. Any help with this?

I know people who are successfully running FCP 7 on Mountain Lion. How much further this 4 year old app will go remains to be seen.

>Can I just buy an upgrade to FCP version 7?

If you can find one on eBay, Amazon etc. Apple discontinued FCS 16 months ago.

>Or will I run into the same problem?

FCS 2009 (with FCP 7) has an Intel installer.

>I may not have to even install FCP 6...as long as I have the Serial.

Correct.

>I also understand that Apple only supports FCPX on Mountain Lion,

I run FCS 2009 without issues on ML. You will get better support on this forum than any offered by the iLife experts staffing the Genius Bar.