QUOTE(lostinyonkers @ August 15 2008, 12:02 AM)

I have been pouring over the Strobist site for several days now, and I am so embarassed to say.... I am stuck all the way back on the "Lighting 101" part because I can't figure out exactly what I need.
I have a Canon 40D.
I have a Canon 420EX Speedlite.
I realize the 420EX doesn't have a PC jack, which is apparently something I need... but I can't figure out if there's something I can buy that will make my 40D talk to the 420EX when it's off the camera. It looks like I need some sort of adapter that I stick on the hotshoe connector part of the Speedlite, but if that's correct, I'm not sure what I should be looking for to buy.
And I'm not even sure if it'll work with my 420EX anyway, since I have such limited controls. Will I be able to work through these Strobist tutorials with a 420... or if I should just give up and buy a 580EX?
I apologize if I sound like a complete idiot. Maybe I'm just having a blonde moment, but these "basics" seem way over my head!
The 420EX does not have any manual settings, nor is it an auto-thyristor, therefore the only way to use it effectively is with Canon E-TTL. There are four ways to get it off-camera and use E-TTL.
One is to use an off-camera shoe cord like the 2 foot long Canon OC-E3. This is basically a cord with hot shoe connections at either end, one end goes into the camera hot shoe and the other end attaches to your flash hot shoe foot. It's only 2 feet long, so it only allows you to mount the flash ona bracket above the camera, or hold it in your hand off to the side. $70 on B&H
The second option is to buy the Canon ST-E2 transmitter. This is an infrared transmitter that mounts on your camera hot shoe. It is not a flash. It will control the 420EX remotely and maintain E-TTL. $220 on B&H
The third option is to buy a 580EX or 580EX II and mount that on your camera hot shoe. It will control the 420EX remotely and maintain E-TTL. The 580 can be set to fire or not to fire, so you have the option of firing the 420 only or some fill/main combination of remote 420 plus on-camera 580. 580EX II is $420 on B&H
Note that for the second and third options above, the built-in flash in the camera does not function as a master unit like the ST-E2 or 580, you have to buy an ST-E2 or 580 if you want master/slave flash capability.
The fourth option, like Dave T says, is to use RadioPoppers. I've never used them. The manual for the RadioPopper P1 says it is combatible with the 420EX. But you need to mount a master unit on the camera, so you would need to buy either an ST-E2 or a 580 in addition to the RadioPopper. So I guess the advantage to the RadioPopper plus master unit is that you go from an infreared trigger to a radio trigger and should gain more range and less line-of-sight issues.
Or you can go manual, like Dave T says, and buy some pocket wizards and one or more manual flashes like the Sunpak 383. You'll need at least two pocket wizards, one on the camera and one on each remote flash. The pocket wizard Plus II runs $188 each at B&H. The Sunpak 383 is $99. I recommend against using optical triggers because your flash will be triggered every time one of the guests takes a picture with their camera flash. That's why you need a radio trigger like a pocket wizard for this option.
You can see that the manual option is not necessarily the cheapest way to get started, especially considering you already have a 420EX. Maybe you should consider buying a 580EX and going with option three, and then if you decide to later go the radiopopper or pocket wizard route, you can always reuse the 580 in that system.