BEFORE TAKING OFF, THE PLT APPEARED TO HAVE DIFFICULTY FOLLOWING TAXI INSTRUCTIONS. HE THEN TOOK OFF WITHOUT CLEARANCE AGAINST CROSSING TRAFFIC. WHEN HE RETURNED TO LAND, HE WAS CLEARED FOR RGT TRAFFIC TO RWY 18. THE ACFT ENTERED A LEFT DOWNWIND FOR RWY 24 INTO OPPOSING TRAFFIC. AFTER THE TOWER ISSUED COLLISION AVOIDANCE ADVICE TO OTHER ACFT, N736HV WAS CLEARED TO LAND ON RWY 24. HOWEVER, THE PLT OVERSHOT THE TURN TO FINAL APCH & MANEUVERED BACK TOWARD THE RWY CENTERLINE.WHILE MANEUVERING, THE ACFT COLLIDED WITH A 70 FT TREE ON RESIDENTIAL PROPERTY APRX 1 MILE FROM THE APCH END OF THE RWY.THE ACFT THEN IMPACTED THE GROUND & SLID INVERTED FOR ABOUT 80 YDS. BOTH OCCUPANTS RECEIVED HEAD INJURIES. THE PASSENGERREMAINED UNCONSCIOUS FOR ABOUT 2 MONTHS AFTER THE ACDNT. A CHECK OF THE PLT'S BLOOD SHOWED AN ALCOHOL LEVEL OF 175 MG% (0.175%).