No additional software is required on a full Slackware 14.1 install.
Slackware 14.1 ships with KDE 4.10.5.

I did a review of Slackware Linux 14.0 a year ago and I was unsure as to whether I should make another one or not. There is rarely much change from a user point of view between different Slackware releases, and I expected to end up ripping off most of my previous review. Speaking of which, for a more well rounded assessment of Slackware Linux, please check out the Slackware 14.0 review.