Why not install KUbuntu from the get-go? It'll all be nicely set up for you and will save any worries of stuff 'under the hood'.
KUbuntu, in case you didn't know, is a variant of Ubuntu but for KDE users.
With regards to your specific apt question. I'm not sure how you would do this. I'm sure Brett or other hardcore Debian users on this list could answer that :)
Cheers, Richard.