typically i would back up to disk and then use network backup software to come get it out of the shared folder that i backed it up into
however to directly backup to a network address
One method is to map a drive to a network location
NET USE X: \\Server\Share
and then use sql backup.
Backup database northwind to disk=x:\backup.bkf
you should however use sp_adddumpdevice to map a backup location to a permanent device it cleans up the backup processes and gives you a fixed location to find all of your backups instead of temporary ones