If the hoses are in good shape and not leaking or showing signs of cracking I'd not replace them. I would get new crush washers for the connections however. Flush the reservior and lines w/ATF before installing the new rack. Remove the return line at the P/S reservoir, start the engine and run a quart through into a container to clear system before pulling the old rack. Once you get the new rack in and everything buttoned up fill with Mobile 1 ATF. Start the engine and turn the wheel from lock to lock and top up ATF if necessary. You may consider replacing the ball joints and conical radius rod bushings while you are at it. Check the 700/900 FAQ under steering rack and bushing replacement for more details. Get an front end alignment when done.