I haven't seen a DIY for that particular housing. Parts are the same and you can get them all at ledsupply.com and digikey.com. If you can reuse the reflector you can save a few bucks.
LED -
http://ledsupply.com/creemce.php
Reflector -
http://search.digikey.com/scripts/Dk...me=711-1067-ND
Driver -
http://ledsupply.com/03023-d-n-700.php
You may have to have a heatsink solution if it gets too hot in the case.
Or you could just gut an mc-e flashlight -
http://www.dealextreme.com/products.dx/category.925
Hope that helps.