IPSec with 2.6.9 and Windows clients

Hi,

is there a good howto for a Linux VPN-Gateway using racoon and IPSec
provided with the actual kernel 2.6.9? Also one for how to set up a
connection to the gateway using Windows XP and the client shipped with it? I´m a bit confused, when do I need also the L2TP (l2tpd)? I thought IPSec would be enough to secure a connection over ethernet but also over internet via ppp (pppoe). But I´ve read that over the internet L2TP is also needed. If someone could explain me what is needed when it would be great for the examples

Linux ------ internet ------ Linux
Linux ------ ethernet ------ Linux
Windows ------ internet ------ Linux
Windows ------ ethernet ------ Linux

Thank´s in advance.