Windows XP VPN server behind Linux gateway

Hi,
The linux box has kernel 2.4.23 and I have added two iptable rules to
dnat port
1723 und protocol 47 to the VPN server in the local network.
Connecting from outside with another winxp machine, also behind a
firewall with iptables and IP masquerading, doesn't work.
I've read that you need kernel patches for 2.2.x kernel versions but
nothing concerning 2.4.x.
Can you give me some tips?
Thanks,
Markus

why not just install pptpd (poptop.org) on your linux box and let it manage
those connections?