THE CAPT WAS COMPLETING THE CHECKLIST DRG PAX LOADING & THE F/O SECURED THE DOOR & CAME FWD. THE CAPT STARTED THE #2 ENG& BGN SINGLE ENG TAXI WHILE ATMTG A RGT TURN TO STAY CLR OF A PARKED DORNIER (N264MC). AS N259MC BGN ROLLING FWD, THE CAPT NOTED THE NOSEWHEEL STEERING (NWS) WAS INOP. HE APPLIED NORMAL BRAKING, BUT GOT NO RESPONSE & N259MC BGN A LEFT TURN. THE CAPT SWITCHED THE HYDR PUMP FM 'NORMAL' TO 'MAN ON' (MANUAL); HOWEVER, BFR HYD PRES WAS BUILT UP BY BATTERY PWR, N259MC COLLIDED WITH N264MC. AN INV REVEALED THE #2 GENERATOR (GEN) WAS NOT CONNECTED TO THE GEN BUS. NO PART MALFUNCTION/FAILURE WAS FND DRG CHECKS OF THE ACFT SYSTEMS. THE NWS & NORMAL BRAKES WERE ELECTRO-HYDRAULICALLY ACTUATED.W/O GENERATOR PWR, THE HYD SYS, NWS & NORMAL BRAKES WOULD NOT HAVE BEEN OPERATING WITH THE HYD SW IN THE 'NORMAL' PSN. AN EMERG (PARKING) BRAKE WAS AVAILABLE, BUT IT WAS NOT USED. THE TRAINING PROGRAM, OPN MANUAL & DORNIER 228-SERIES PILOT OPERATING HANDBOOK DID NOT ADDRESS SINGLE-ENG GROUND OPN OR THE EFFECTS OF AN INTERRUPTION IN GENERATOR PWR.