Windows – What setup allows a Windows 7 client to use OS X 10.6.7 server VPN with L2TP

Why not set up L2TP if you don't want to harden PPTP further? There are a plethora of guides on the internet on setting up VPN using AWS free service micro tier instances and Ubuntu.

Here is one article from the AWS support forum with a discussion and links to how-to articles for setting up L2TP over IPSec on Ubuntu:

https://forums.aws.amazon.com/thread.jspa?messageID=286936

OSX Server does have several VPN servers in it. You can configure these using Server.app however, if your internal name resolution is broken this is likely to be more trouble.

You'll also need to make sure your Mac Mini's VPN port is available to the internet on a static IP (or dynamic host name).

As an interim step I suggest looking at 'Back To My Mac' which is free as part of iCloud. Technically it uses adhoc ipsec vpn tunnels and gives you an DNS name for each mac set up, effectively bypassing the current internal name resolution issue. e.g. server.12345678.members.btmm.icloud.com Services that you run e.g. web and ssh will accessible.

They're btmm DNS address are not internet routable and don't, generally, require any port forward or static IP addresses. For a couple more technical details check here: https://apple.stackexchange.com/a/53776/46039