I'm not familiar with Mandriva, as I use Fedora almost exclusively. Fedora, like Mandriva, is RPM-based. I use a program called
yum to manage my software. It is extremely easy to use. Also, I believe that there is a graphical version of it called GYUM as well, but I haven't used it.
Well, after a little Googling, I found out that Mandriva has a graphical package manager with it. Once he gets that up and running, he'll should have no problem installing software.