tell application "Finder"
    set theFolder to ((path to desktop folder) & "Images") as string as alias
    set myImages to the name of every file of theFolder
    set indexOfFolder to (count items in myImages) as number
    set newName to "whateverName" as string

    repeat with x from 1 to indexOfFolder
        set name of item x of theFolder to newName & x & ".JPG"
    end repeat
end tell