Yes, you can use a 580EX II as a master to trigger a 430EX II as a slave, without the 580 firing during the exposure. Press the Zoom button on the flash so that you see the blinking 'on' then turn the dial to show 'off', then press Set. Note that the 580's master function is optical - you'll see the on-camera flash fire as a preflash which signals the slave flash(es), but the on-camera flash won't fire during the exposure.