Thanks for the PM, but it would be better if you respond in the thread so that others may also benefit.
So you have two SCO 5.0.5 machines that you want to have mirror each other.
If you are looking for a magic bullet, forget it.
SCO have solutions based on 5.0.7 and Unixware, that will provide this kind of product if you need minute by minute redundancy.
If you can live with once per hour or per day mirroring then use either NFS or FTP to copy the changed files from the primary system to the backup system.
An alternative is to add transaction logging to your application on the primary system, and have a background process on the secondary machine post those transactions to the data files on that machine.