If you have set up Mint 4 Daryna with a separate /home partition, it should be easy. When you are in the partitioning phase of the Mint 5 Elyssa install, do not put a check mark in the "format" box for your /home partition. That will leave all of your personal files untouched. It is always a good idea to back up those important files, just in case. I have some friends who have had the same /home folder through several upgrades. It can be done and works pretty good. Your kilometerage may vary, however.
That being said, when upgrading from one version of an operating system to another, say Mint 4 to Mint 5, I copy my important personal files to a flash drive, then format all the partitions for a clean install between versions. I then drop my personal files (documents, pictures, music) back in the /home folders. If I have to reinstall my operating system while using the same version for any reason, I do not format the /home partition. I format the /root partition and everything cranks right back up to its normally fully-functioning state.
My reason for not carrying over a /home partition intact is there may sometimes be variations between versions that might not work exactly right due to carrying over previous preferences and options settings. I do not keep /home versions intact between different distributions (using the same /home partition for openSUSE and Mandriva, as an example) since I have concerns for that being a recipe for disaster.
Now, if you did not originally set up a separate /home partition, you may have to research a tad further in the forum for the exact method you possibly need to use. I do suggest basic manual partitioning for your next Linux install since it should give you much more control over your system. It is an excellent idea that you are already planning ahead, and I do wish you good luck.