This is but one way to skin the pptpd cat but it may help those wanting a pptpd VPN server on their Centos 5 server?
I use yum where possible rather than compile from source, so add the relevant poptop repo as follows: rpm -Uvh http://pptpclient.sourceforge.net/yum/s ... noarch.rpm
Yum install kernel-devel Note: if you are installing pptpd to a xen kernel then yum install kernel-xen-devel as well.
yum install kernel_ppp_mppe dkms ppp pptpd (I got some errors about the old ppp_generic module which I have ignored for now without any obvious consequences so far) Note: if ppp is already installed from the Centos Base repos you will need yum update ppp to get the RHEL5 version which may in turn require you to unprotect your Centos Base repos possibly breaking compatibility with the upstream provider blaa blaa. Make your own decisions here.
edit /etc/pptpd.conf (particularly the ip address ranges to suit your LAN)
default /etc/ppp/options.pptpd should be fine
chkconfig pptpd on (if you want the VPN server to start on system startup)
open TCP/UDP 1723 and GRE 47 on your VPN server firewall
service ppptd restart
fire up your fav vpn client PC etc, create yourself a vpn connection and see if it worked for you