Some backup utilities (Backup Exec, for instance) include a server agent for UNIX (including SCO). This is a small utility which is installed on the SCO box and listens for connections from the Windows system during backup time.
If that isn't an option, you have others:
Create compressed tarfile on the SCO box using CRON, then throw it over to the Windows box using FTP (pre-setup required on the Windows box to allow that to occur).
If the SCO box has VisionFS, you can create a mount point to a Windows share and put the tarfile there.
Since both of those options include making a tarfile first, you must have enough free disk space to do so, and you are likely limited by the 2GB filesize limit (depending upon your version of SCO).
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