I never got a chance to build mine, ordered the parts just didn't have the time to put it all together. Will do when I get the chance though.

Well I don't mean to sound cocky but you can do it with one transistor, 1 resistor and 1 pot;

Code:

+12v  ------>|-------,
(unreg)     LED      |
                     |
                     |
+5v  --------,       |
             |       |
             |       |  NPN (or Darl)
   500 ohm   R       C  TIP122 etc
      pot    R<----B    
             R       E
             |       |
             |       |
             |     Rload  4.7 ohms 5w
             |       |    (etc)
             |       |
Gnd ---------*-------*--

This is a constant-current dummy load, adjustable with the pot from 0A to about 1A, depending if you use 3.9 ohm or 4.7 ohm for Rload.

It will drift 1 or 2 percent as the transistor warms up, which is rarely an issue.