HELP: can't initialize iptables table `filter' ????

[Sim]

I've read all of the online documentation but can't really understand it.  I
want to masquerade my c	able modem connection.

I'm using kernel 2.3.99-pre3 and the April 3 iptables 1.0.

I've built as modules 
-rw-r--r--    1 root     root        22227 Mar 31 21:06 ip_conntrack.o
-rw-r--r--    1 root     root         3716 Mar 31 21:06 ip_conntrack_ftp.o
-rw-r--r--    1 root     root        16884 Mar 31 21:06 ip_tables.o
-rw-r--r--    1 root     root         2096 Mar 31 21:06 ipt_state.o             

and then insmod-ed them all.  But then any iptables command just leaves me with

 iptables v1.0.0: can't initialize iptables table `filter': No extended target/match by that name
Perhaps iptables or your kernel needs to be upgraded.

For the masquerading, I was planning to use the following (based on the NAT
howto)

  iptables -A POSTROUTING -t nat -o eth1 -j MASQUERADE 

eth1 is the network card connected to the modem.

I expect I should just be playing with this kind of technology if I don't
understand it, but I want to prepare for the 2.4 kernels, and also need to use
2.3.x to get my webcam going.  ipchains had been working fine for me up until
now

Simon