I have been looking at the 35W model.
http://www.trailtech.net/eclipse_mr16.htm
They seem really nice, especially for the price.
Nice small, water tight, internal ballast.
Drawback, they arent that effecient.
Dont get me wrong, they are ALOT more eff. than an incan bulb,
but they arent as eff. as D2 bulb setups.
Should make a great bike light though,
10AA would work I think, but with voltage sag, you should probably use 12 cells.
I have emailed them with a few questions, including what the actual voltage range is.
but I have not gotten a responce yet.
~John