looking for a versioning file system

I'm really not sure where to post this, so I apologize in advance if I should have put it somewhere else, and trust that someone will move it to where it belongs.

First, a little about my home setup: My family has a mix of machines on our network, running XP, Vista, and W7 (plus one rarely used machine running W95 for an old favorite game we can't get to run properly on anything newer). Years ago, when replacing an old XP machine, instead of just trashing it, I decided to reconfigure it as an El Cheapo file server, reinstalling XP from scratch and adding a large (for the time) hard drive, most of which is shared over the network. Over time, I've continued to add disk space as needed, but kept to a minimal OS install.

Now, most of our family has come to rely on this shared storage space, as a means of accessing their stuff from whoever's computer happens to be closest instead of having to run to their own machine all the time to get things done. However, in the past month or so, I've had three instances where important, frequently edited files have had to be rebuilt from backups because of various communications errors or other glitches that occurred while saving updates to them.

I've come to the conclusion that it's probably time to demote some other machine to this file server role (which I'll probably be doing some time after the Christmas gifts are opened ), but it seems inevitable that THAT machine will also start acting flaky some years from now, and cause some future files to need to be similarly reconstructed. My question is, can I get and configure some sort of versioning file system for this machine so that with minimal (ideally no) forethought on the part of the end users, any file that is updated has the previous version automatically saved under an alternate name, and if another glitch occurs, we won't have to reconstruct more than the last session's worth of changes to it?

Thank you for the suggestions, but I already do backups; I'm looking for a better solution - one that doesn't require people to "do" anything. I want something that will automatically back up the old version of a file, at the moment the new version is being created. That way, if the new version turns out to be total junk, the latest old version is still available, even if it never made it to a backup location.