How do I restrict USB access?

I am the system administrator on a network using a single Ubuntu 12.04 computer as a server and several Windows (XP) clients.

Is it possible to restrict users from accessing USB storage devices on their Windows machines from the Ubuntu server?

Note: These machines may have other non storage devices connected via USB such as keyboards and mice which must not be affected by this.

I am aware I can block access on a client by client basis from the Windows side by following the instructions from Microsoft here:
How can I prevent users from connecting to a USB storage device?

But I want to be able to enforce this from the Ubuntu side.

Is this possible and if so how?

Unless there is an extra client-server system in place, I read from your question the following.

You have a network with several computers, used as Windows clients, and a computer used as Ubuntu server. These computers have no special relationship, they just 'are' on the network. Now you want to disable the "use USB storage devices" feature on the windows computers

Then no: your 'random' ubuntu computer (that currently is designated 'server') cannot force another computer to restrict USB access. That's all local. The computer itself must do this.

Now solutions could be the windows OS setting permissions. It MUST be from the windows side. What you can do is have your windows computers 'look' for a master (domain server for instance) and that server set the policies. But the you'd still need to change the windows machines, and I know of no method to set windows policies from Ubuntu...