Two copies of a program... Remove one?

Hello. I have a used Power PC G4, replacing my old G4 that gave up the ghost. It has OS X 10.4 installed, but it also contains the hard drives cannibalized from my old Mac, on which I find two copies of ProTools, one of them version 5.1.1 dated 2001 and definitely dating from my old Mac, and - on a different hard drive - version 6.4 (expressly specifed on its CD as for OS X), either dating from my old Mac or recently installed, I can't remember.

Should I simply delete the old one? I'm mostly experienced with PCs, and relatively new to Macs. A friend told me all I can just delete it - that (unlike PCs) I don't have to go through a separate uninstall program. Is that true?

(Neither of these two hard drives is the one that OS X boots from. When I run another OS 9 program from one of those drives, an OS 9 emulator loads, and the program seems to run successfully. )

Currently, I'm experiencing the following behavior:

- Clicking on the new version of Protools (6.4), I receive an error message saying that it could not be launched because of a "shared library error".

- Clicking on the old version of Protools (5.1.1), I get no error message at first (no complaint about a shared library), but then it reaches a certain point and complains that the DAE is not found. It's been a while since I've used my Digidesign Digi001 (an item of audio hardware - owned by the Avid company), but I believe this message is referring to that. However, my Digi001 *is* plugged in to the Mac, and its power light is on (which it does not when it is not plugged in - there's no separate power supply).

What should I do, and how?

Thanks for your help!

Peyton