route based on incoming eth out ppp - two eth / two ppp

I have two ethernet connections to an internal lan and two
outbound connections via ppp - two seperate isp's

I need to be able to route traffic based on incoming source.

25
------->| eth0 | --------->ppp0 ---------> Internet
| 80 |
| |
| 26 |
------->| eth0:1 | --------->ppp1 ---------> Internet
8080


I have two squid and two sendmail daemons running each
bound to it's interface.
Outbound mail needs to be able to go through it's
respective isp's smtp server as a smart host - hence
the traffic shaping.

I have scripted the connection and then added the following
iptables setup. Unfortunately it is not working.

#/bin/bash!
p0=`/sbin/ifconfig |grep P-t-P | awk '{print $2}' \
|sed -e 's/addr\://g;' |grep 209`
p1=`/sbin/ifconfig |grep P-t-P | awk '{print $2}' \
|sed -e 's/addr\://g;' |grep 129`
#
echo $p0
echo $p1
# Setup IPTABLES
iptables -t mangle -A PREROUTING -i eth0 -j MARK --set-mark 20
iptables -t mangle -A PREROUTING -i eth1 -j MARK --set-mark 21
ip route add default via $p0 dev ppp0 table 22
ip route add default via $p1 dev ppp1 table 23
ip rule add fwmark 20 table 22
ip rule add fwmark 21 table 23

Can anyone see where i have made a mistake in this?

Thanks for any and all help,

Cheers,

Chris