If you watch the Super Browser 2 Turbo HD Remix talk from Google IO '11 there is a bit in there about developing something very similar, though less robust, to pre-load the assets. The core concept is the same as pre-loading image rollovers in JavaScript. Not a library, but the talk and slides give a decent overview of the code.
http://www.google.com/events/io/2011/sessions/super-browser-...