First of all, you need to define the IPsec Policy, look under "local security policy" or if your admin implimented GPO, then look under that to define necessary level of encryption. 3 default settings are Client, Server, and Secure Server. You canalso create custom setting for your needs. You need to define that first, and apply IPsec Policy to RRAS and the Client computer.
Assuming you don't have any trouble getting rest of the stuff, like actually have clients connecting without IPsec, U need to specify if you want your RRAS to be Router, RAS/VPN server, or NAT server. If you are going to use IPSec, you need to use L2TP (Layer 2 Tunneling Protcol). L2TP encasulates the packet, and IPsec encrypts it.
For your dialup connection, its going to use PPTP (point-to-point tunneling protocol). It doesn't have the 128bit encryption, but it has 40 or 56bit encryption and unfortunally for u, doesn't have the option of using IPsec. So, dialup use PPP with PPTP, and networked (such as AT&T broadband service) can use L2TP with IPsec.
Sorry, its a long answer, but its very complicated subject. For me, I have enabled the IPsec communication for LAN, but not like what u want. Its a very tricky configuration, and i don'trecommend doing it unless u're just testing it out. Also, having RRAS in your network increses the administration and create headach if not configured correctly. I suggest reading this book "Network Infrastructure Administration" from Microsoft, Chapters 5, 11 for more detailed info.
Laterz
