How do I do Time Machine backups for multiple computers? I have 4 Macs that need TimeMachine backups; they all run Snow Leopard, and it's unlikely that they will be upgraded to Lion/Mountain Lion anytime soon. 

Currently, they are all backed up to a bunch of drives set up in a RAID array, but it causes me a fair amount of pain every time a drive fails (which happens somewhat frequently).

Is there an easier way to do this? I'd prefer not to use a Time Capsule, since we need to have a NAS anyway, and I'd prefer to only have one set of technology to maintain.
You question is a bit unclear. How do you back them up to the NAS currently?

Time Machine can backup to network drives On supported NAS machines so you need to check with your NAS vendor for the particulars. The other option would be to have one of your Macs host all the Time Machine backups.