Setting up a L2TP/IPSec VPN server on SBS 2003

Hi
I need to know how to set up a L2TP/IPSec VPN server on SBS 2003 so that mobile users can access the corporate LAN from their WinXP laptops. I understand there are more then one way to acomplish this. But i’m looking for the simplest/easiest one. All help is much appreciated.

Note: I know that the easiest way is by using PPTP but it in my case it HAS to be L2TP/IPSec.