If you want a smooth install it will be best for you to back up your programs to an external HDD or DVD and then do a full erase of the old OS, reformat and install Leopard. Many people have had issues doing an Archive and Install when doing an OS upgrade. It's really not a good idea to use Archive and Install or the Upgrade option, you may have stability issues. You are mixing old files with a major OS upgrade, it's best to do a full erase and install.
Archive and Install is best used when you are reinstalling the same OS. The Upgrade option is best used when you have a clean install of the old OS and you are just upgrading to the new OS.