Rule #1 - When in doubt, always back up your files
Rule #2 - Even when not in doubt, back up your files
If you created a separate /home partiton upon your original install, then you should be fine. All you have to do is choose the same partition as a /home partition and make sure format is *not* checked.
My understanding is that if there are multiple users on the current system, you will have to recreate them in the same order you did originally.
If you created one partition (a / partiton only) then you will have to backup all your data as you will loose everything in the /home partiton.
I would conquer a previous poster on a previous thread, create a /media/data and house all of your personal data there. You can even take it a step further and create that partition as a FAT32 partiton and you can access it from windows if you dual boot.