At the console that it boots to, login as the root user (superuser) type
Hit enter, and if everything is set up correctly it will take you to a login screen. If it doesn't work, you should get some error messages you can copy and paste in a message to get help.
Setting it up to automatically start kdm is a little more complicated. I don't remember how to do it off hand, and you would be better off getting that advice from someone who uses Mandriva.