Robby updated his KDE 4 package for Slackware. New updated dep are included in the proper directory. You can find the package at the usual place located here. Here is the changelog
Updated Mon May 19 20:59:16 UTC 2008 –rworkman
These packages are for Slackware 12.1 – DO NOT bother trying them on
any earlier releases of Slackware, as they will not work.
kde-4.0.74 is not intended as a replacement for the stable kde-3.5.x
series; rather, this is a development snapshot of what will eventually
become 4.1.0. The next snapshot is expected to be beta1.