Mac Mini and Pro Tools 6.0

Hi Folks,
I am new to the Mac world, and have a mac mini OS X 10.4.2 and I am trying to set up my M-box with Pro Tools 6.0.

Everything installed just fine with the exception of the fact that when I try to enable a track to record, I get a message along the lines of "this volume is not enabled for audio" (not a direct quote).

I hav googled it and tried various things, i.e. verified permissions on my drives (tried both the internal HD and an external hd. Both are read-write enabled.

I shouldn't use the internal system drive for recording (when I tested it it gave me the above error) and my external also gives me the same error.

I am guessing that I should be using a firewire external drive instead of a usb.

Can any of you guys give some advise?

Many thanks!!!

Red