you should be using Stuffit 5.1.3 for OS 9
, search keyword 'Stuffit'
as for your other problem(s), try putting the Finder Preferences file in the TRASH and restart and reset Finder Pref's in Edit menu...
This works for many many strange conditions that occur in the Finder, it is a STANDARD 'trick', well-known and well-used.
IT MAY NOT fix your problem but it is a start and you can come back here (as I am sure you will) if you need more help