I have 2 computers networked over a crossover cable and 2 ethernet cards sally and sue
I can shh to eather one from the other
and ping back and fourth betwineen the two computers
now sue has another ethernet card conneced to a ADSL router (using DHCP )
this is my inter net connection
SO
I want sue to share her internet connection with sally
how do I do this ?

We'll assume that sue is running Linux. If so, you need to do several things:
make sure that the network segment connecting sally and sue is using a Private Networking address range;
enable ip_forwarding on sue;
set up Network Address Translation on sue;
go read about how to set up a firewall to protect this lash-up from the bad guys out there on the Internet.

Fortunately, I have written a bit about this on my website: http://www.digitalelephant.org/
Follow the menu there for Linux Config/Network Setup/Address Translation. Other parts of the Network Setup section may also be of interest.

This is one way to do it... make sure to change the ppp0 to the correct label for the card that is plugged into the dsl.

#!/bin/bash
/sbin/modprobe ipt_MASQUERADE
/usr/sbin/iptables -F; /usr/sbin/iptables -t nat -F; /usr/sbin/iptables -t mangle -F
/usr/sbin/iptables -t nat -A POSTROUTING -o ppp0 -j MASQUERADE
echo 1 > /proc/sys/net/ipv4/ip_forward
/usr/sbin/iptables -A INPUT -m state --state ESTABLISHED,RELATED -j ACCEPT
/usr/sbin/iptables -A INPUT -m state --state NEW -i ! ppp0 -j ACCEPT
/usr/sbin/iptables -P INPUT DROP
/usr/sbin/iptables -A FORWARD -i ppp0 -o ppp0 -j REJECT