おい喜べ。できた。
tell application "System Events"
tell application "System Preferences"
activate
set current pane to pane "com.apple.preference.energysaver"
end tell
tell process "System Preferences"
tell window 1
tell group 1
click checkbox "可能な場合はハードディスクをスリープさせる" of tab group 1
end tell
end tell
end tell
end tell