I agree with Buggabill: works for me in Chrome 5. (At least on the server; there may be issues with loading files from a local filesystem.)
However there are problems with your approach. By having page content loaded by script only, you have made your page inaccessible to non-JavaScript users, which includes all search engines. Also you can't use the back button and the pages are unbookmarkable, un-open-in-new-tab-able, and so on.
Basically you've reinvented all the problems of <frameset>, the reasons why no-one uses frames any more. You shouldn't really deploy this kind of solution until you are familiar with the ways accessibility and usability can be served. At the very least, you need to point the navigation links to the real pages containing their content. Then consider allowing hash-based navigation, so the dynamically-loaded pages have a unique URL which can be navigated between, and which will re-load the selected page at load time when the URL is first entered.
Also if you are loading content into the page you should take care to load only the content you want, for example using load('portfolio.html #somewrapperdiv'). Otherwise you are inserting the complete HTML, including <!DOCTYPE> and <head> and all that, which clearly makes no sense.
To be honest, as it currently is, I don't see the point of the dynamic loading. You have spent a bunch of time implementing an unusual navigation scheme with many disadvantages over simple separate navigable pages, but no obvious advantage.