Looks to me like you've forgot to include jQuery, since you're including a version of History.js that's built for this. Without including jQuery before jquery.history.js, the latter will fail.
EDIT:
After including jQuery before jquery.history.js, do window.History.pushState(null, "Title", "/url");
. Notice that History starts with a capital H, this is important.
See my fiddle for how to use History.js. I've only tried it with Chromium, but see if that works in IE8 for you.