A BE-400 flight crew declared an emergency and returned to their departure airport after experiencing the failure of the Horizontal Stabilizer De-icing system.

Narrative

I was the Second-in-Command and pilot not flying on this leg. The weather was 2;000 overcast with moderate mixed icing reported. We had flown two previous legs earlier on this day using our engine Anti-Ice; Wing Anti-Ice; and the Horizontal Stab Deice with no abnormalities. The Anti-Ice/Deice systems all checked out on the ground.We were cleared for takeoff and at 400 FT the Captain called for flaps zero. We turned to a heading assigned by Tower; and I turned on all the Anti-Ice/Deice systems. We immediately got an 'HSTAB ICE FAIL' light. The Captain requested an immediate return to the airport. We declared an emergency and requested an altitude of 2;000 FT; which would keep us out of the clouds. I informed our two passengers that we would be making an immediate landing because we had lost our deicing protection. I accomplished the Horizontal Stabilizer Ice Protection System Failure checklist. I then accomplished the Flaps 10 Approach and Landing Procedure checklist.We landed at Flaps 10 without further problems.