You didn't mention what OS you had previously and what your new one is. Here is a link to the compatibility list. Make sure you have the correct version of PTLE to go with your OS
Yah, Digi001 is only good up to system 10.3.9 - if your "friend" installed tiger, you need to go back. Or create a new partition with an old 10.3.9 system on it for dual-booting when you need protools.
I changed the OS already from Tiger to Panther and I have disks for Protool 5.1.1. Protools got upgraded to 6 something. Do I need to remove that version before I reinstall the older version? Will installing the Protools disk allow the computer to recognize the 001?