Several readers responded to my Aug. 28 column, "Easing the pain of an upgrade," by suggesting that a tape backup can facilitate the job of moving files from an old computer to a new one. It can help but won't do all the work. The tape drive can save time. First, copy files from your old hard drive to tape. Then, install the files on your new machine, either by using a compatible tape drive or by moving the same tape drive from one machine to another. The hitch involves Windows programs, especially if you have customized touches that you want to move to your new machine. You will have to reinstall many Windows programs for them to work properly. The process is trickier if you are moving to a machine with Windows 95 installed.