[belese]

It's maybe due that your source.list point to brantje repo,
and some apt error aren't check,
so apt-get update fail, and xbian-config have no new package.

try this, and retry :
http://www.xbian.org/faq/
the part : (] The APT repository at xbian.brantje.com seems to be unreachable)

otherwise you can check log in /tmp/aptstatus ((from head)