Or, if you don't WANT to screw with configuration files, you simply do one of the following:

#1. Easiest... Type "init 4" on Slackware, and "init 5" on everything else in Linux, and it loads the GUI log in screen which is normally KDM or GDM (KDM for KDE based stuff, and GDM for Gnome, but you don't have to pick Gnome from it).

#2. At your login prompt, log in, then, type one of the following:

kdm &

or

gdm &

or

xdm &

You get the idea. That loads one of those GUI log in thingers that let's you log in and select the GUI you'd like to use when you log in. KDM and GDM both ask if you want to make the X Window Manager the default for log ins after you've selected one, so it can remember it for you too.