Accessing older OS thru external HD

Not sure where to stick this, but this looks like a good spot.

So, I got the G4 tower here and i've been using it for about 8 months and I've really come to love it and so I got a powerbook. I came across another G4 tower once, and grabbed the hard drive from it and hooked it up with a USB cable and could still access the programs and stuff that were on the OS. Sort of. Some would, some wouldn't. But I think a bunch of them were OS9. I can't be sure and i've already reformatted the drive and moved on.

But... I got mad programs and settings and stuff set on this Mac and I don't quite remember how I did it all. So I was hoping that I could hook up the HD from it with the USB cable to the powerbook and access everything and adapt as I go, as it were. Is this going to work? Can I open and run programs, explore settings and add-ons and essentially virtually run the old OS on the "now external" HD as if it were installed on the powerbook?

The powerbook is running Tiger and the HD is Panther.

yes you can, assuming the Powerbook is a G4 or G3, not Intel.

And assuming the copy of 0S9 is compatible

Just use the Sytsem preferences to set the start-up disk, if if wont boot disconnect the external and re-start. Once back in to your POwerbooks drive you can reset the start-up disk to the powerbook.

OS9 also has a control panel to set the Start-up drive when you want to move back to OS X