switch(screen.availWidth){case 640:

break;case 800:
window.self.moveTo(0,0);window.self.resizeTo(800,600);

break;case 1024:
window.self.moveTo(0,0);window.self.resizeTo(1024,768);

break;window.self.moveTo(0,0);window.self.resizeTo(1280,1024);

break;}