MYF Controller described a loss of separation between two arrival aircraft when; unobserved; a LGEZ overtook preceding traffic and landed with only 1;000 FT separation; the reporter indicating the LGEZ acted inappropriately.

Narrative

A LGEZ was inbound from the west and issued left traffic for 28L. He requested 28R and I acknowledged his request and issued 28R. About that time; a Biplane called from the west and requested Runway 23. I issued him a left downwind for 28L with his request acknowledged. I had one PA32 on final for 28L; plus one PA28 and one PA44 in the north pattern for 28R. This is not busy traffic for a Saturday afternoon. To accommodate the LGEZ's request; he was instructed to pass behind the PA28 on final for 28L; and follow the PA44 for 28R. He reported both aircraft in sight and acknowledges the clearance. In the meantime; I issued instructions for the other pattern guy to extend and turned the Biplane to a left downwind for 23. The PA44 was issued exit and instructions short of 28L. I could not find the LGEZ in my scan and realized too late that he had closed the distance between the PA44 too rapidly. He was in the flare with the PA44 about 2;500 FT ahead. I issued a go-around; maybe twice; and they acknowledged but were already committed to the landing and could not abort. They rolled out about 1;000 FT behind the PA44 exiting ahead. Recommendation; the LGEZ did not maintain spacing even after reporting traffic in sight and being instructed to follow. Furthermore; the pilot landed with another aircraft on the runway ahead; which I find to be a bad practice. Not being a rated pilot; I can only speculate as to why they did this instead of going around themselves. The Biplane distracted me because he was wishy-washy about his intentions once he heard the actual winds; so I had to clarify things with him. In my preparations to accommodate his request for the crossing runway; and fit him in between my other traffic; my scan was diverted to the ACD (ARTS Computer Display); and him; to ensure he was turning at the right time to make it flow correctly. When I scanned the spacing on final; the LGEZ was rolling out about 3/4 of a mile behind the PA44 and the spacing looked good. Obviously he was faster than I realized; and he did not attempt to follow. All in all; had I scanned sooner back to my final; I might have seen he was eating up the PA44. I am very proactive in my scan. If I had not been accommodating the Biplane's unnecessary request; perhaps I would have been scanning the runway instead of watching the PA28 and the Biplane to make sure I built the hole; it would not have happened. I will be much more reluctant to accommodate silly requests; but Biplanes have already cracked up two planes due to 'crosswind landing issues.' As for the LGEZ; I will not move people to 28R when the wind is down 28L. They can learn to land on a skinny runway instead.