Added later: See the following post (above) for solution!
First, the good news. I have Leopard up-and-running, and it is great. It feels faster (maybe it is faster, who knows) it looks great.
Installation is supposed to be straigtforward. Put the CD in the drive and follow the instructions. We got to the place where you are supposed to select a disk on which to install Leopard - no disk appears. Wait,... Wait some more,... Make a cup of tea, ... Still a blank.
Go back, and look for an exit button - there is none. Try Disk Utility as suggested to select startup drive - no drive appears. Despair begins. I did back up my important files before starting this process, but restoring them will be a hassle - and what about the unimportant ones (I have a long tail, lots and lots of not very important files, but if they all go, that will feel quite important).
I try various incantations of keys (escape, eject, command-Q, even ctrl-alt-del) nothing works.
In desperation, I plug in an external drive to see if I can perhaps escape this nightmare by installing Leopard on that. The drive appears, but I'm not allowed to install on that drive. I'm about to do a hard reset (well forced power-down by pressing the button until it gives up). Then, my hard drive appears as a possible selection.
I select the drive, hit continue, and leopard installs without further hitch (it takes almost two hours).
It looks just the same - it just feels better, and faster. Of course, if you look closely, it isn't the same, but the changes are subtle, it feels entirely familiar, but better.
Now to install XCode Tools... This time, everything starts fine, but then fails at the end telling me that CHUD installation has failed, and I should contact the software manufacturer (that would be Apple).