Thanks Oscar, I'll give that a try and let you know how it goes.How about this?
If you boot the CD with puppy pfix=ram it won't look for any save-files or ask if you want to upgrade them. Do that, run the installer and install into a new "slacko5.6" subfolder. Then add the generated lines to your grub4dos menu.1st file. Shut down without saving, remove the CD and reboot. The Slacko 5.6 should now be an additional boot option (make it the default if you want) and you can create a new save-file to go with it leaving the old ones intact until you are ready to ditch them later or keep them or whatever.
And thanks again, bigpup, it's good to know that there are plenty of people with plenty of suggestions for solutions, cheers all.