One of the best first questions I have seen so far. Usually we get, "where can I get a laser that will start my school on fire?" or "how many watts does it take to blind someone I don't like?"
Your question isn't stupid at all!
Also, different diodes require different voltages AND different currents. As a rule, the longer the wavelength, the lower the voltage. It will also depend on what kind of battery you want to use.
If you want to use two 3.7 v batteries to drive a red diode then you need a driver that can buck (decrease) the voltage in addition to supplying the correct current for the diode.
If you want to use a low voltage setup, lke two AA's at a total of 3v then you need a driver that can boost (increase) the voltage as well as provide the correct current for the diode.
Hang on, I'll get a post that explains it really well.
EDIT:.
http://laserpointerforums.com/f67/f...river-tested-working-71433-8.html#post1033246