Great difficulty with Leopard on Quad G5, teeth are gnashing

[Adam Bridge]

I'm having a seriously not very good time getting Leopard to go on my
quad G5. I'm grumpy.

I fortunately have a good backup, unfortunately I've had to restore
from it TWICE.

The first time was my bad - I did an update instead of "archive &
install". I meant to do the archive but somehow I neglected to choose
that option. The result was a system that was frozen almost
immediately after restart.

Archive and Install did somewhat better but I'm still ended up with a
frozen system where nothing was responsive.

How do I trouble-shoot this? Or do I just bite the proverbial bullet,
install from scratch and then re-install all my software - CS3
Extended and Final Cut Studio are non-trivial installs, time-wise, and
I'd really really REALLY not have to do that.

As I think about things I've added to my system only one waves any
sort of red flag: I have a weather station attached to my computer and
it uses a USB to Serial device that needs a driver. Unfortunately I
don't remember where that was installed (it was years ago) nor do I
remember where to look for it. So a suggestion there might be good.

Thanks for your thoughts.

Adam