Decrease OS X system volume with AppleScript (can be used in Alfred2 and QuickSilver to make hotkey and use it on non Apple keyboard to control volume)

Volume Down

set curVolume to output volume of (get volume settings)
-- work out the new setting
if curVolume > 6 then
	set newVolume to curVolume - 6
else
	-- can't go over 100
	set newVolume to 0
end if
-- and apply it
set volume output volume newVolume