Sorry, I'm more of a command line junkie.
There's a file called /etc/fstab. It contains all your mount points for partitions and whatnot. There's a column where you can specify options and for things that should be mounted every time you boot, you enter the option "auto" as one of the options.
Your graphical tool probably has a similar "check box", but since I haven't ever used Mandriva you may have to search for it a bit. Or you can post your /etc/fstab file and we can help you modify it to auto mount at boot time.