Thanks, I've added the apt source and updating apt-get and that worked fine.

But I haven't got KDE installed at the moment, and so apt-get dist-upgrade has no packages to update. I tried to install KDE by doing this:

apt-get install kde

But I get a lot of 'depends' errors like this:

Depends: kdelibs3 but it is not going to be installed
Depends: kdebase but it is not going to be installed or kdebase3 is not going to be installed

And lots of other releating to KDE.

Do you know how I can fix this mess?