The difference between apt and urpmi on Mandrake is that urpmi is tested for Mandrake. You shouldn't install apt because you don't need to install apt. All it does is complicate the setup process. For anybody who is interested in using Mandrake/Mandriva, I would suggest reading the other howto, http://www.howtoforge.com/perfect_setup_mandriva_2006. Even if you are installing 10.2, there are very few differences between that and 2006, and that howto actually does things in a way that won't break Mandrake.