Is it possible to store backups from ACS 5.1 to an external machine on the network. We would like to store our ACS backups on our backup server.
Yes. Backup can performed to a repository and there are options for FTP, NFS repositries that will allow the backup filers to be shipped off board
Yes, you can store it on some server on your network, just define a repository pointing to it, using FTP or SFTP as needed.