Some information would be helpful. Is your /home directory in the same partition as the root filesystem, or is /home in a partition of it's own?
If /home is in it's own partition, just don't touch that partition when you upgrade Mandriva. All of your personal files/settings/preferences/bookmarks will be preserved. If you mess up and format that partition, it's all lost. Word to the wise: make a backup before upgrading (such as an .iso archive of the /home folder burned to CD/DVD), just in case you do mess up.
If /home is in the same partition as the root of the filesystem, make a backup of /home (copy it to another disk or burn it to CD/DVD) then restore the files to /home after the upgrade.
Other files to backup: any files in /etc that you have spent a lot of time tweaking, any databases that you may have created, along with the grant tables.