startx should do it, though you should not need to. Did you change the install type when installing?
Assuming you get KDE from startx, then click on the lizard in the corner (for your start menu). Go to "Control Center"->"System Administration"->"Login Manager"->"Administrator Mode"->"Convience" and select your login.
If that doesn't give you an auto login on reboot, then go to YaST->System->"Runlevel Editor", and make sure that xdm is enabled.
If you don't get in with startx, then something is really not setup right. Chances are X isn't even installed then. Post back if you have more trouble.