Hi. We've got a site where a lot of the editors are using IE8. We found that jscalendar did not work in this context, because it was using browser detection to see that it was dealing with an IE browser, and then handling it thusly, rather than treating it as a standards-compliant browser.
This is a fundamental problem with the idea of browser-based detection. If you want to see whether the browser supports addEventListener, check to see if that function exists.
The actual symptoms of the problem were: Clicking on the calendar image would cause the calendar to pop up, but clicking on any of the dates would not cause them to be entered into the input field.
I've got a patch that marks IE8 as a non-IE browser, and starts to implement capabilities-based detection. Using this patch, it was possible for me to use the jscalendar in Firefox, IE7, and IE8.
IE8 support