Server 2003 Ent. VPN Issue

I have a Server 2003 Ent. box currently being used as a terminal server through remote desktop. Some of the users need to use the VPN (PPTP) function to access some files correctly. I set the server up for RRAS in accordance to microsofts website, but I cannot the server to accept incoming connections. For testing purposes, I have 2 points DMZ hosted, but still no luck. I am running WinXPProSP2 on the client machines…. anyone?