I haven't done one of these conversions- but a lot of folks here have posted their experiences. Use the "Search" function (top of the page), and search on the term 'mini mag' in the LED forum, searching titles only. That should give you a wealth of reading info.
You'll probably need at step-up regulator for any 2AA minimag mod. I've tried directly replacing the maglite bulb with a 3mm white LED - and the light is worse than an Infinity's! Just barely enough to read a newspaper by at 6 inches with new batteries.
With the regulator, you'd be able to run a Luxeon Star! yummy....
Use a couple of Energizer Lithium AAs and you can get pretty decent performance out of a single 5MM Nichia LED in a Mini-mag in a super easy conversion.http://az123.com/darksbane/do_it_yourself.htm
It may not be quite as bright as the ones with a DC - DC step-up circuit, but a lot easier to do.... It won't be as bright as one with 3 N cells or something like that, but will last longer, and provide more than enough light to get around in the dark.