What you're talking about is technically called the Display Manager
or "DM", and is commonly also called the "login manager".
You are presumably using GDM (the GNOME display manager), and want to change to KDM (the KDE display manager). There is also XDM (the X display manager, non-specific to either GNOME or KDE), other "loose" DMs, such as entrance
, and Mandrake has a specialized version of KDM known as MDKDM (not that you care, using Slackware as you are, but you did ask if there are others, and there are).
As for how to change your DM, that is controlled by /etc/rc.d/rc4
. It looks first for GDM, then KDM, then XDM.
You can either just uninstall GDM (so it is not found; GDM is a separate package from GNOME, so uninstalling it should not affect any GNOME installation you may have, though I can't speak for a Dropline GNOME installation, which is slightly differently configured), and then Slack will be forced to default to KDM, or you can comment out the three "Search for GDM" lines in /etc/rc.d/rc4
, so that they are skipped and Slack just starts KDM.
I suppose you already know that KDM can be configured through the KDE Control Center
Hope this helps.