It’s prob. more of an OS issue,
in the Finder, select any .psd file and do a Command-I to “get Info”
You’ll see a section named “Open with:” and a pop-up to choose a program.
Select Photoshop CS2 from the pop-up (or if it isn’t listed via the “other…” option)
and then click on the button “Change All” to open all .psd files with PS CS2
You may need to have administrator privileges to pull this off, I believe.