are you just looking to make a backup of everything or are you looking to move the system to another box?

I usually use the -depth command to make sure it gets everything.

log in
cd to /

find . -depth -print | cpio -ocBv > /dev/rStp0


If you are looking for something to keep backing up your system I would look into lonetar or backupedge. their products work great with SCO and both of the products allow you to make Rescue Disks. These are a set of floppies that you can boot from, that will access the tape drive and then allow you to restore your system to a blank disk. It will even divvy the disk back to what it was.

good luck.