Instead of backing up individual client machines (bad!), you should be doing a couple of things.
1) Network home folders w/ offline cache enabled (OS X calls this a Mobile Account, I believe). This will alleviate the need to backup a bunch of individual client machines. You just back up the single server and all of their data will be there.
2) Automated deployment solution. Something like ASR or Deploy Studio so that when a machine craps out, you can reimage it quickly and to a known configuration so that the users can be back up and running and accessing their network home folder immediately.
The combination of these two things will both simplify your backup and make you more agile in the event of a client laptop failure.