A BE-40 flight crew rejected their takeoff due to loss of directional control; two flat main gear tires were discovered and the flight subsequently canceled.

Narrative

Normal taxi-out procedures and checklist usage were executed. We were cleared into position for immediate takeoff. Pilot not flying completed the runway items checklist; pilot flying cleared the area as he taxied into position. All indications were normal as the power was advanced. Normal callouts were made; at approximately 80 KTS; we noticed the aircraft losing directional control. Abort was initiated prior V1 and the PF did his best to maintain control of the airplane on the runway. Airplane came to a stop on the runway; to the right of the centerline. Abort and after landing checklists were completed. At that point it was also noted that the parking brake was verified in the 'released' position. Tower was advised of our abort and disabled situation on the runway. Company; FBO; and Maintenance were called to accommodate the passenger and facilitate moving the aircraft. Upon inspection both main tires were flat; and maintenance changed the tires and removed it from the runway.