harrowc, if you setup the vpn in sbs via the wizard, it will not ask your for NAP ;
I did this just today and my clients connect from anywhere and sbs is the vpn server (PPTP), i just checked the NAP mmc and it isn't configured
I would recommend, to remove the vpn role from your server and then use the vpn wizard to configure it ; in network > connectivity tab
Which is why I posted the link which does setup the vpn server without NAP through the wizard ; it seems that you didn't configured it via the wizard.
Let me know if you need further help on this.