Driver suggestions for 1 XM-L on 4AAs?

I replaced the emitter in an old 3AAA Dorcy with a T6 Cree XM-L and I get awesome light but very little run time on the AAAs. I have a battery box for 4AAs from an old Petzl headlamp that I'd like to hook up to the XM-L to improve the run time. Can anyone direct me to a driver that will work well with this combo? I will mostly be using NiMH batteries, so the input voltage will be between 4-5V. Not postive what current I want to run it at yet, but whatever the Dorcy put out should be fine.

Thanks!
Tim

shiningbeam.com has a good 2,8Amp driver. 2.8-6V

Awesome. The 3 mode up to 1A should work great for my purposes. Pardon my ignorance, but how do you switch between the modes? Do you set it once or can it be controlled through rapid switching or something?

Thanks!
Tim