At 2108:57 EA Flight 275 (EA275), a Boeing 727, was cleared to take off on Runway 19. At 2110:24, N6509V, an Aero Commander, was cleared to taxi into position and hold. N6509V entered Runway 19 near mid-field at Taxiway A-3 without advising the tower of his intent to depart from an intersection. The captain of EA275 saw N6509V entering the runway; however, he stated there was insufficient time to abort the takeoff. He veered slightly to the right and began an early rotation in an effort to miss N6509V. EA275's left wing tip struck the right wing of N6509V, causing substantial damage to N6509V and minor damage to EA275. The crew of EA275 was unaware of the collision and continued to Seattle without further incident. Night VMC existed at the time of the accident. Considerable snow removal activity was in progress on taxiways between Taxiway A-3 and the north end of Runway 19. The local controller did not verify the position of N6509V before clearing the airplane onto the runway, and the ground controller did not monitor the taxi route of N6509V. Traffic was light.