Before you begin to install or upgrade software, import your data into newer versions of programs, or convert data to run under different programs, make sure you have at least two current copies of your data. Since getting your computer ready for the year 2000 may involve some or all of those potential problem areas, back up your data before you start. Better to be safe than data-less. The choice is up to you. Floppy disks are cheap, but the number needed for a complete backup of your hard disk might seem excessive.
Zip drives offer another option.
Tape backup systems are available. While all of these options involve some expense, keep in mind the cost of recreating, if possible, the data you might loose. If you can re-install the original software, you might think about just backing up your data. If you store your data on floppy disks, make sure you make copies on other floppies and, perhaps, a hard drive as well. And, for those who have access to network drive space, using some of it to store backups makes sense as well.