It doesn't show, but a 3 way switch will control a circuit from 2 locations only.
If you want 3+ locations, you will need 4 ways wired in between.
2002 NEC says you have to have one at each room entrance (not including hallways), so if you've got 3 doors, you need two 3-ways and one 4 way.
Just to clarify a bit... The top half is showing the entire circuit as if it was hooked up. The "PANEL" is the source of electricity (fuse, circuit breaker, whatever), the "LOAD" is what is being powered (light, outlet, fan, etc). The bottom half is showing what is going on inside each type of switch. On a 3 way, the "COMM" (Common) is where you hook in the "Constant Hot" (first 3 way) and the "Switched" leg (last 3 way).
The "Neutral" always passes thru boxes that contain normal switches w/o stopping. The "Ground" pretty much does too, except it grounds the metal parts of the junction box itself and the switch to protect the user from electric shock in case something grounded out inside and energized the metal case.
Coming from the panel, you will have 3x ("3 by") Romex/equiv or 3 seperate wires. These wires are:
"Constant Hot" (Black), obviously has 120V at all times.
"Neutral" (White), is the return path to the panel*
"Ground" (Green), is to prevent from electric shock
Now, between the 3 ways (or between 4 ways), you need 2 "Travellers" to allow the switches to work properly. To obtain this, you will use 4x Romex or 4 seperate wires. As before, the Neutral and Ground pass thru (with the ground grounding stuff on it's way). At any given time, one of the Travellers will ALWAYS be hot, so they need a "Hot" color (black, red, blue, etc)
"Traveller" (Black)
"Traveller" (Red)
"Neutral" (White)*
"Ground" (Green)
You may use whatever "Hot" colors you want for the Travellers, but it will usually be Black and Red since that's how Romex is colored (3x has black, 4x has black and red, etc).
From the last switch to the lights, it goes:
"Switched" (Black or White)
"Neutral" (White)*
"Ground" (Green)
If you want to control the load from 3 or more locations (as many as you want, actually), you will hook a 4 way into those travellers. You can add as many 4 ways as you like, but there must ALWAYS be two 3 ways at either end.
*NOTE that the Neutral may not be present at the switch boxes... in this case, the neutral will pass straight to the load... Need to be careful when messing with wires, because the NEC does allow the white to be used as a "Switched" leg. This means that in a switch box, you will only have 3 wires present at the switch... Constant Hot (black), Switched (white), and Ground (green). There should be tape/paint/etc marking the conductor as current carrying, but that may be missing.
However, I don't think the NEC allows the white to be used as a traveller, but I could be mistaken... it would save some $$$ if they do since if the neutral isn't present at the switches, you will have an extra wire if you buy 4x.
Now if y'all want, I can draw out how the 4 ways work in different "UP" and "DOWN" configurations, but for now, I'm going to bed! 
