Thanks for the response. Ten years was a slight exaggeration. Only slight though, but I think it was in 2003 or 2004. Original version was 2.1 or 2.2 I think.
I think the original OS was 9. It still had the older GUI that you could run within the OS. At that time, it was a G3 or G4. I've upgraded machines several times since then, switching to Intel when it became available. This is the third Intel MacPro tower system I've run it on (3.1.8, 3.57 GHz, 24G RAM, dual quad-core). I've moved the disks from an older Intel system into the newer one, and have done that each time I'd gotten a newer bigger Intel system.
I updated, upgraded FCP each time, eventually repurchasing the package with both PowerPC and Intel packages (I think that was version 5.1), and continued upgrades via downloadable upgrades since.
I did not try to open both at once. Just the older version (not FCPX). Prior to upgrading to Mavericks, the application worked, and did not ask for the serial number to run. After upgrading to Mavericks, it now asks for the serial number, and none of the serial numbers I have attached as stickers on the Installation brochures which came with the installable media are accepted as valid serial numbers.
Hope I'm making sense.