i second George's comment about losing weight off your body first.

The BEST weight saving mod you can give yourself is a fast lightweight aero set of wheels. I increased my avg speed from 18mph to 20mph by switching from mavic open pro's to cane creek aerohead teams. The reason that wheels make such a huge difference is because rotating mass is more important than "dead" weight. And also the wheels are a significant factor in aero drag, because they have a relatively large frontal area