Hi
It is a sad fact that files that are deleted across the network are deleted for good. As suggested above you can restore from backup, but apparently there are a couple of programs out there which will help prevent this from happeneing in the future (you will need to search TechRep for this - I cannot recall where this information is).
We recently redesigned our network and installed a 'linkstation' which is essentially a NAS device which plugs straight into the network. One of the features of this device is that anything that is deleted via a client is automatically stored in a hidden 'Trash' folder. This has come in very handy as it saves restoring from backup tapes.
Of course - you would still need to backup the data on the NAS anyway, but the trash folder is definately a bonus.
Good luck