Mount root of SMB Server
There's no root in Samba protocol. To list shares on your server you can use smbutil(1):

$ smbutil view //Administrator@10.211.55.8/ | awk '$2=="Disk"{print $1}'
ADMIN$    
C$        


and then use output with mount_smbfs(8):

smbutil view //Administrator@10.211.55.8/ | awk '$2=="Disk"{print $1}' | while read sharename; do 
  mkdir ${BASE}/${sharename}; 
  mount_smbfs //Administrator@10.211.55.8/${sharename} ${BASE}/${sharename};
done


Please, read man pages to check other options I haven't used here.

The best utility to make backup I know is rsync(1). You can found it from MacPorts. It'll be interest if you know better.