Web application - Midi synthesizer

I want an application like [login to view URL] except I will need some customizations. If you can do the front-end, I can handle some back-end processing modules myself. Knowledge of midi files is a must (thought if you are generally interested in music and a good programmer, you can learn midi format easily). You can recommend the choice of technology (java applet/ flash/others) depending on detailed discussion with me. regards, JP