Would radiant heat be enough heat in a basement made intirely of nudura ICF? in utah, and about 1800 sq feet?  and if so how do most people cool thier basement if they arent using a forced air system and just radiant heat?

Sure, if designed properly.

Around here, A/C is typically accomplished with a central forced air a/c system regardless of type of heat.

Look into the split A/C sysytems with the compressor outside & an air handler on the wall . The ICF wall will stabilize temperatures so heat from windows is the major effect to watch for in sizing A/C