Make that 3 of us. I am having the exact same problem as josiane:
24" PPC 2.1 GB iMac running 10.4.8.
If I open Photoshop 7 from a Finder window, it opens Switch. Ditto for Image Ready. Also the treble clef icon.
Photoshop opens from the Dock, however Image Ready in the Tools pallet is dimmed.
I've tried:
repairing permissions
running Yasu to clean out caches and such
and
repaired the directory with Disk Warrior.
none of which helped.