The easiest way to get KDE3 is to use packages from here:http://slackware.osuosl.org/unsupported/kde-3.5.10-for-slack13.0/packages/
This is not an optimal solution though, as these are old, unsupported versions.
The future of KDE3 is with the Trinity project. We are working on building that suite, but it is a big undertaking. No guarantees that it will be a good fit for VL7.
I just installed KDE3 using these packages, and so far, no issues. For several months I've been running these same packages with Slackware 13.37 on my old laptop, with no issues.