ip masquerading module problem

[Q]

Hi,

# I have installed YDL 2.2 kernel 2.4 (rebuilt for network card realtek 
rtl8139), set up my
# ADSL internet connexion (pptp & ppp on eth0) which works fine but I 
can't get my ip
# masquerading to work.
# I have followed the howto I have found on this website:
http://jack.info.unicaen.fr/cgi-bin/dwww?type=file&location=/usr/share/doc/HOWTO/en-html/IP-Masquerade-HOWTO/index.html

# I have configured the
 /etc/rc.d/rc.firewall

# but when I call the file I get the following error (and few others):
Enabling SNAT... ...can't initalize... ...tables 'nat' does not exist...

# after a bit of reading I have tried this:
insmod iptable_nat.o
# and get this error
iptables_nat.o: unresolved symbol xmon

That's it I'm blocked
Any idea?
Thanks
Q