Hy, I've installed slackware 10.2 right now and had the same problem... It's quite annoying.
After a bit of googling I came on this page:
http://wiki.kdenews.org/tiki-index.php?p…nfig%20Settings
which is about things that aren't GUI configurable.
basicly, you have to edit a file named:
~/.kde/share/config/konqsidebartng.rc
adding:
ShowArchivesAsFolders=false"
at the START of the file.
hope it's useful to others too, it was a bit difficult to find out.