Hi Max; Yes, if you want to use /dev/hda5 as the /usr directory then you must choose to initialize "another partition" during the installation otherwise all of the files normally destined for /usr (quite a few) will be copied to /usr on the root filesystem.
If you were to later initialize /dev/hda5 and then mount it on /usr all of the existing files in /usr "become hidden" and are unavailable to the system. While it is possible to copy the contents of root's /usr to the new partition first it is not even close to as trivial a proceedure as it might seem.
