On August 31, 2000, at 1316 central daylight time, a Piper PA-28-236, N451X, operated by a commercial pilot, experienced a left main gear brake fire while taxiing for takeoff at the Des Moines International Airport, Des Moines, Iowa. The pilot was not injured and the airplane was substantially damaged. The 14 CFR Part 91 flight was operating in visual meteorological conditions and an IFR flight plan was filed. The intended destination was Bloomington, Illinois. The pilot reported that he was taxiing to the runway for takeoff when the airplane slowed "as if it were taxiing uphill, or a brake were dragging." He reported that he added about 100 rpm of power to continue taxiing. The pilot reported, "When I attempted to set the brakes to check the engine and instruments, I found that I had no brakes." He then contacted the ground controller and requested a clearance to taxi back to the fixed base operator on the airport to get the brakes checked. Another pilot, who was on the same frequency, announced to the pilot of N451X that his airplane was on fire. The pilot reported that he looked and saw dense, dark smoke coming from under the left wing. He reported, "I immediately shut down the engine, turned all switches off, and exited the airplane. The fire was in the area of the left landing gear-almost directly under the left wing fuel tank." An inspector from the Federal Aviation Administration Des Moines, Iowa, Flight Standards District Office, examined the airplane. The inspector reported that hydraulic fluid was found on the ramp where the airplane had been parked for several days prior to the accident. He reported that he was unable to determine exactly where the fluid was leaking from, due to the extent of the fire damage to the landing gear.