We are officially beyond the extent of my knowledge of apt-*..
IIRC Natty is still a beta release, maybe package that is causing it to hang is broken/missing/etc?
Maybe if you try changing to a different mirror in /etc/apt/sources.list ? (if there is one for natty)
Perhaps it is possible to download and update the problematic package manually? maybe build from source?
$ sudo apt-get clean
$ sudo apt-get check
Other than that, sorry mate, im fresh out of ideas