Cisco VPN with a Microsoft PPTP client

I have a small office with only workgroup computers and a single Cisco 837 ADSL router as the internet connection. I have been assigned the task of providing remote access to the office. A requirement of this is that the VPN clients must be Microsoft PPTP and the VPN server must be the cisco device, but also we must have access to the internal network behind the router to enable remote desktop to the PC’s.

I have been unable to find any information on doing this. I can only seem to get info on using a cisco VPN client.

If anyone has done this before or has any ideas that would be great.