Well your first problem is that there is an upper limit of 10 concurrent connections that will work on any Peer to Peer Windows Network and less if you are not using the Pro versions so if there are any XP Home units involved they will only support 5 concurrent connections.
The way to perform a back up in this situation is going to be a bit harder as you'll have to do it from each machine individually well maybe you can do it fro a couple at a time but then you run the risk of having some of the connections staying put and not dropping off which could be a problem.
AS far as Scripting goes as this is an All Windows setup you can use VB [b]I can't believe that I just said that.[/b]:(
And then map the drive one computer at a time and backup to an individual folder for that computer and once that is finished have the script drop that computer and move on the the next one with a different target folder although all the target folders can be Sub Folders of one folder. You'll need to remember to target the My Documents Folder the Address Book and E-mails for backup as well as any specialized programs that don't store their data in the My Documents Folder on XP/2000. The favorites list may prove useful as well but that all depends on the use that these computers are set to.
As VB is notoriously unreliable I wouldn't push the upper limits and if the network is fast enough this shouldn't be an issue if you do one computer at a time it will also cut down on network traffic and allow faster individual backup to be taken from each individual computer.
That's the way that I would do things but now we have to address the actual scripting and depending on how much you know this can range from an easy to difficult option.
A good starting point is most likely here for the basics involved
http://tinyurl.com/4h52e
