If you cannot use HTML5 (Canvas and SVG), then you probably need to revert to one of the good old plugin based solutions. A very mature and performant platform is Silverlight, although people tend to call it deprecated in favor of HTML5 - the same holds true for Flash (Flex) based solutions, and of course the good old Java applets. For all of these platforms there are open source and also commercially backed closed-source solutions available:
http://www.google.com/search?q=silverlight+diagramming+control