So recently I was searching on google on how to setup a PPTP VPN server in linux, specially in Debian OpenVZ VPS. I own few low end vps from BuyVM and Ramnode. Both are 128MB vps and allowed TUN/TAP and PPP.
After some search i got few sites that actually has the perfect guide of OpenVZ vps. This will help you a lot. I have personally tested on both of my openvz vps and successfully able to connect pptp vpn from my Android phone and windows 7. Works great.
These are following sites that will help you create a PPTP vpn server in Debian / Ubuntu.
http://www.putdispenserhere.com/pptp-vpn-setup-guide-for-a-debian-openvz-vps/ (Tested & Recommended)
There is also a script that will automatically setup PPTP/PoPToP on your OpenVZ VPS in a few of minutes. Port forwarding, server configuration, and authentication setup is all taken care of for you.
http://www.putdispenserhere.com/pptp-debian-ubuntu-openvz-setup-script/ (Tested & Recommended)
For troubleshooting this link helped me: