Good luck with the project. I posted a few weeks back to see if anyone had tackled a DIY divelight, but recieved no response.
I found a site a few months back which wetted my appetite, and being of a mechanical engineering back ground, I thought "I can do that!"
Have a look at
http://insel.heim.at/malediven/350052/english.htm
Its not an "English" site and some of the translation means reading between the lines, but the general gist is there.
I am currently sourcing materials to have a dig myself.
My initial idea was to "bastardise" one of those El Cheapo 500,000 candle power rechargeable handlamps (Blackspur-£9.99) found in many car accessory emporiums. Then I saw those Dichroic (spelling?) lamp units in B&Q, 50mm dia units with a range of 2-pin halogen bulbs rated from 20W up to 75W with varying beam angles and thought of mounting one or two of those in some thick-walled plastic or Ali tube, reed switch/magnetic slider for on/off and lithium ion rechargeables.
As they say in management circles "Lets kick it around a little" and see if we can rattle up something useable for a cost of under, say, £100.