Use Modernizr for detection of feature capabilities. In general jQuery offers to detect browser features: http://api.jquery.com/jQuery.support/. However, hashchange is not on the list.
The wiki of Modernizr offers a list of libraries to add HTML5 capabilities to old browsers. The list for hashchange includes a pointer to the project HTML5 History API, which seems to offer the functionality you would need if you wanted to emulate the behavior in old browsers.