I have a vpn server setup that acts as a gateway for remote users. They desired function is for them to be assigned the servers public IP address for changing their IP's geographic location. This function works fine, but I do not want them to access resources on the local network or access each others files. I know this is the opposite of typical a pptp's intended use, so I am having trouble finding the right answer. How do I block client to client communication?

Thanks for any help!

As far as I remember, the PoPToP server (or you're using something else?) has an option which allows/disallows client-to-client communication. But I may confuse these parameters with ones of OpenVPN.

You may also use firewall, as all traffic will go through the server anyway. I'm sure this solution will do its job.

ps: I've checked the official website of the poptop project and haven't find any appropriate options.
The only one which seemed to me more or less useful is proxyarp, you can find the description: http://poptop.sourceforge.net/dox/options.pptpd.txt
But I'm not sure (due to weakness of my English ;-) if it's what yu wish to have.

Thanks Lexus45, this may be helpful, I will read up on it more.

Anyone know of an iptable rule to block this communication?

Thanks again!

PPTPD will create an additional interface in your system.
Try to firewall on it, using the FORWARD chain in the "filter" table. I hope you know your clients' IP range.