Radial calipers are suported radialy, ie at the front and back of the caliper on the same radius from the axle for each support. Normal calipers are typically supported with 2 fixings at the front of the caliper. If you look back to back at a pic you will see what I mean.
Pads in radial calipers are less prone to pad suck. They supply a more even pressure across the whole surface of the pad than conventional calipers.
Whether they are that much better for the average rider on the road I don't know, they look good though.
[Edited on 30-6-2005 by Herb]