How to use an off camera flash and wireless flash trigger at the same time?

I want to use the AlienBees B800 with a Yongnuo RF-603 as a wireless flash trigger for my Nikon D90. Will this be possible since the RF603 will occupy the hot shoe slot on my camera? Where do I plug in the sync cable for the B800 on my camera?

If you are using radio triggers, you don't need a sync cable - that's the whole point of wireless triggers - no wires! You have one RF603 sitting on the hotshoe (this acts as a transmitter) and another attached to the Alien Bee via the 6mm jack.

There should be available (if it didn't come with it) a short cord that plugs into the RF603, with a 3.5mm jack plug - it may or may not have a 3.5mm to 6mm adapter on it too, if not you'll need to get one. This then allows your second RF603 to plug into the AB.

You did buy 2 RF603's? You always need at least 2 - one on the camera & one on the flash.

I have RF602's but they're v.similar (except mine are separate receivers/transmitters, mot a multifunction transceiver).