David,
On your Windows box, create the directory you want to back-up to. Make it shared. On your e-smith server, create a mount point in the /mnt directory and then edit /etc/fstab (the file system table) and add an entry for the share you made. Mine is below (all on one line):
//p133/Backup /mnt/backup smbfs username=name,password=password 0 0
//p133/Backup is the server/share in UNC format; /mnt/backup is the mount point; smbfs is the filesystem type (samba file system); the username/password combination is your Win98 system login. The last part relates to the filesystem type (I can't remember the details, but the man page will help you).
After you've done this, you need to set up the /sbin/e-smith/backup script per Darrell's suggestion, using the e-smith template system. If you want to adjust the scheduling of the backup (for example, I only want mine to run weekly, not daily), the appropriate cron entry can be found in /etc/cron.d
Good luck!
Des Dougan