Unfortunately the Flash Player on N900 is version 9, but current version on other platforms is 10.1 (and 10.2 beta was recently released for desktops). We probably won't get any official update, so more and more sites will block us from using Flash.

As RAZOR said there is a app that can fake your flash version. This only works for flash applications that don't use any 10.x features seriously. It's worth a try.