Beige G3 question

[Gordon Neault]

Before you try the other fixes mentioned, there is one obvious thing to 
try.
MacOS will not install an earlier version of the OS over a newer one.
The fix is to open the system folder, drag the "Finder" to any other 
location (a new folder, the desktop, whatever) and restart with the 8.5 CD.
  If there are no other problems away you go.
As far as I know the iMac CD's install on anything. A more likely problem 
is that the G3 requires a minimum version higher than your 8.5 CD; in 
general you need the same version it shipped with but there are exceptions,
  so give it a try.