Windows VPN connection throuh Linux router

I think i almost got it but i'm not quite there
I'm trying to make a VPN connection from a windows XP machien to an XP machine. I have the VPN server side setup at PC A and i have PC B connecting. Right now PC B can get as far as verifying username and password and goes no further.

Ports i have forwarded to PC A from the linux box (which is my router) are 1723, 500, 47, 50, 51

using this method:
$iptables -A FORWARD -p tcp -i eth0 -d 192.168.0.3 --dport 1723 -j ACCEPT
$iptables -t nat -A PREROUTING -p tcp-i eth0 -d 69.xxx.xxx.xxx --dport 1723 -j NAT --to-destination 192.168.0.3

i do that for every port i forward.
the setup of my VPN server side is right, cuz i've tested connecting locally and it works, anyone see what i'm missing?

Linux distro is Redhat 9

Thanks for your help!

does it work with encryption ?
if it is so it wont work via NAT.

well yes... microsoft's VPN uses encryption so if what you say is true, then I scrap that idea and try to setup vpn server on the linux box. I have done this now but maybe not correctly.

i setup PopTop and the remote user was able to connect to the linux box, but he cant ping the linux boxes internal IP or any ip in my network, i can ping the IP he connects to the lan using though, i set the server to use a range from 192.168.0.15-90 and he connected with .15 i could ping with average ms of 37ms. he cant ping anything to our end though so somethings not quite there. i'm stuck:/

Err... 47, 50, and 51 are protocols, not ports (at least in this case).

[chort@abydos ~] grep -E "47|50|51" /etc/protocols gre 47 GRE # General Routing Encapsulation esp 50 IPSEC-ESP ESP # Encap Security Payload ah 51 IPSEC-AH AH # Authentication Header

In particular, you need to allow all GRE traffic through your firewall.