I use the 580EX II and 430EX II as Master and Slave respectively with no issues. I gather you already know that the 430EX II can only be used as a Slave; the 580EX can be used as Master or Slave (if you have another Master flash or an ST-E2). The setup was pretty simple for me; set the 580EX II to "Master" and the desired channel, then set the 430EX II to "Slave" and to the same channel as you set on the 580EX II. The 580EX II has to be the flash mounted to your camera's hotshoe or Off-Camera Shoe Cord (e.g. OC-E3) (at least if you plan to use TTL) and the 430EX II is your remote flash. Canon Speedlites use infrared (IR) controls (as oppose to radio frequency (RF) like Pocketwizards), as a result there are some limitations: your flashes have to more-less be in line of sight (or in a position that IR can be bounced); also using the flashes outdoors in bright sunlight can be an issue as the sun's IR spectrum can overpower the speedlites'. I found the instructions and illustrations in the 430EX II manual to be helpful for setting up a Master and Slave rig.