If you are just dimming some LEDs, just use Pulse Width Modulation (PWM) 
with a FET or BJT.

EG fully on: -------------------
fully off: __________________
50% on; ----_____-----_____-----

where --- = power applied and ____ = power off

Al

I'd like to have my microcontroller (8051) control a
0-12V DC output voltage with up to 1A. It doesn't
have to be accurate (e.g. 8bit is enough) and it doesn't
have to be very clean - it's for an LED illuminator
controller.

I know I could use a linear regulator and an D/A
converter or a digital potentiometer but I'm wondering
if it would be better to use a switching regulator so
I don't dissipate so much power.

Any example circuits how to control a switching
regulator? Any suggestions for devices? I've been
looking at some Maxim chips but I'm not sure how
to connect up the feedback input with the output
of the D/A converter.

Thanks for any hints,
Andrew