I need a VPN solution for my company. One requirement is to be able to use the built-in windows VPN client. We are running a Debian Etch server.

I've managed to set up PPTPD but the authentication is based on the chap-secrets file. We already have all the user accounts set up on the server, so it'd be nice to use PAM authentication to get user/pass directly from the unix login.

Is this possible to achieve and how? If not, is there any other VPN solution that can do this? Don't tell me OpenVPN, it needs additional software to be installed on the Windows machines.