Gatt,
use backup exec system recovery first of all, it's the beefed up version of Norton ghost, and takes 10 minutes to restore a totally knackered server to back and working. We use that for all 36 of the servers here, along with backup exec to backup both FULL backups on weekends, and incremental every other day which are backed up like following;
Previous 7 days are stored on external hard disk for quick restores, previous 40 weekend FULL backups are on tapes, and 4 sets of 7 tapes for weekly incremental backups, so we would restore from the full tape, then incremental to Wednesday using the weekly tapes.
Not sure if that made sense.
It is a per server basis, most simple way would be use backup exec for FS, SQL and Exchange and just Backup exec recovery for AD and DOM controller, what would be the point of backing up individual files on a AD Domain controller? it rarely changes in any major way, so exec recovery is a cheaper option and offers the ability to restore rickety tick in the event of system downtime.
£1,226.97 for the 3 copies of backup exec and £300.99 for exec recovery for the AD server grand total £1,527.96.
Hope this helps.