there is a bug in kpackage that the KDE guys doing bother to fix(for at least 6 months ths reporting by different people). You cannot be root when you want to use kpackage but only ordinary user. Beside, the root must have password as kpackage would do a 'su' to do the real work.

I use kpackage to browse package available and use apt-get for actual installation.

it is just :

apt-get install <package name you see in kpackage>

the dependency will be handled automatically. However, apt-get's logic(or could be that the maintainers logic) only allows easy 'upgrade' and not as good as it sounds in the tutorial that you can upgrade/downgrade anyway you want. There is quite some restricitions once you moved up, not easy to come back down to the old version.