I have used Mandriva for several years now, so let me see if I can help you out.
Linux terminology is quite different that the way windoze does things. In short, I think you should set the 5 gb partition to /. The larger partition should be set to /home.
Here is why. The '/' represents the root, or the beginning of the file system. This should allow you to install the main system files to this partition. This will include the boot files, and all system files. Most of your programs will go to this partition as well.
/home is where your user directories go, for each user. All your user data files can go here as well. Things like pictures, music files, movies etc.
You are given many more choices, linux is all about choice.
This will give you a good disk layout to start with. When the install is done, you will find many directories have been created under /. For example, you will see a /boot, /bin , /mnt and the list goes on.
Here is what my root '/' looks like.
bin/ dev/ home/ lib/ media/ opt/ root/ sys/ usr/
boot/ etc/ initrd/ lost+found/ mnt/ proc/ sbin/ tmp/ var/
This probably seems confusing at first. Linux names things differently than windoze. In windoze you have a C drive and D drive etc. In linux the first disk is called hda ( hard drive a ) then hdb and then hdc etc. On a drive the partitons are numbered, hda1 hda5 hda6 etc. ( 3 partitions on hda.
The file system can be installed anywhere the user likes. So if you tell the installer to install to the 5 gb partiton labeled as /, and the user files go to /home.
Hope this helps.