VPN specialist, Linux

HI, I am retail VOIP service provider. Need assistance is setting up a VPN server, Linux and windows. Currently I have both Linux (centos) and windows 2003 VPN server. I have 2 types of FXS VOIP devices with PPTP functionality: Device ‘A' works with both VPN. On windows I did not had to do anything additional, it just works, the condition is that windows based VPN should be on a 2003 server and 32 bit. On CentOS I had to change the encryption to 40 bit and that worked. Device ‘B’ works on windows, but not on linux. I need a VPN specialist / professional guy to understand the difference in both devices and vpn it supports and make it work for me on Linux. Kindly contact me on my Skype ID surajv7 to discuss further / quarries.