tell application "Finder"
set selectionList to the selection as alias list
if (count items of selectionList) ≠ 1 then
beep
return
end if
set selectedItem to (item 1 of selectionList)
if (class of item selectedItem) is alias file then
set selectedItem to (original item of selectedItem) as alias
end if
if (class of item selectedItem) is not folder then
beep
return
end if
--
-- selectedItem is now an alias to a folder
-- do stuff with it here
end tell
Notice that this script allows you to select a single item which must be a folder or an alias file to a folder.