I have Logic 4.8 and 5.51 for Windows XP, Logic 8 Pro on a G5 and Logic 9 Studio on a Nehalem Mac Pro. Notwithstanding the possibility that mysterious things can happen with archaic files, especially if you are talking about a Power Mac 7200 [?], I agree with Senor Eli.
I was unaware of the pivotal position 7.2 holds regarding Intel/PPC flexibility, thanks for the tidbit.
I tried loading an old Logic demo file, named ES2. On load I got a message: Instrument "USB Port1/CH" sends to a MIDI port named "Port 1" of MIDI interface "HDSP9652" (Slot-3)" which no longer exists. However, there is a port of the same name at MIDI interface "Unitor8/AMT8." Do you want to reassign [, etc.]? That message came up a few more times, and I reassigned it. That told me I have not run this file for a while, because the RME card was moved to a different computer ages ago.
Then, I got the "New SMPTE frame rate recognized, use it?"
The transport kept running, which required opening Logic's "Project Settings." I use an Aardvark master clock, so I changed from an MTC sync mode to "Internal" -- changed the frame rate to 30 (that is a setting on the master sync [MOTU DTP]) -- and also unchecked "Auto enable external sync." That let me stop the transport.
I would have to fire up an XP system with 5.51 to see where I got the demo, but I recall it came with 4.8 Gold, although not sure, it might have come with 5.1 Platinum (which I later upgraded to 5.51).
The demo is a disco, seventyish piece, but has some interesting environment artifacts as well as a nice demo of nine screensets. There is a wave file for it that I did not include. The point is, 5.51 files read into Logic 8 no problem. If it was a 4.8 file, I may have converted it from 4.8 to 5.51 way back when.
As I did not include the "wave" audio file, if you want to audition the piece, you must add the ES2 hybrid synth to each of the indicated tracks.
When I uploaded the Logic session, it was automatically "zipped" -- it seemed to unzip by double-clicking after it downloaded...let me know if there is an issue.
When the file loads, it will tell you the audio file is missing. Click "Skip." Load the Logic instrument ES2 on tracks 1 to 14. Track 15 is an audio track if you want to do a bounce. Track 16 has some meta data: if you want to let Logic flash explanations about the ES2, as the demo plays, unmute track 16. Open the mixer and pull down any tracks that are higher than 0dB. Pull the Outputs 1-2 track down to -6dB to eliminate any clipping.