Stuart, I'm afraid your model of router doesn't support vpn server capability in native firmware by Netgear. However you can 'reflash' your router using the OpenWRT project.
http://wiki.openwrt.org/toh/start#netgear
This will give you vpn dial-in capability.. If you dont want to do that, then your options are somewhat limited to the following.
1. Buy a new router which supports VPN dial-in *Draytek Models do*
2. Build a separate VPN server and put it behind your Netgear router and setup Port forwarding (I would suggest an OpenVPN based on since they're the most straight forward to use on a Mac).
If you need any help doing this, I can assist, the above assumes some intermediate networking knowledge and having been through this kind of thing myself a good few times, I can help.
Regards
dan