Version: (using KDE 4.1.1) OS: Linux Installed from: Fedora RPMs - user is in sudoers, may execute "everything" via sudo (and using his own password to auth against sudo) - KDE in some cases (e.g. administration) requests root-priviledges, however does not seem to use sudo as the users own password is not accepted, separate root-password is required
this is not a plasma issue, and is an installation issue. kdesu, which kde apps use to elevate priveleges in this case, needs to be compiled and/or configured to use sudo rather than su. it does support this, however.
Sudo is not configured by default in Fedora and thus using sudo in kdesu is a no-go.