iptables/netfilter on the 5600?

I installed the iptables ipk from
http://www.killefiz.de/zaurus/showdetail.php?app=1296 on my 5600
(Sharp ROM 1.0), but when I run "iptables -L" (or -A or whatever) I
get the error

modprobe: Can't locate module ip_tables
iptables v1.2.8: can't initialize iptables table `filter': iptables
who? (do you need to insmod?)
Perhaps iptables or your kernel needs to be upgraded.

Indeed, lsmmod doesn't show anything iptables-related.  My desktop
linux box, for comparison, shows

iptable_filter          2348   1  (autoclean)
ip_tables              14648   3  [ipt_state ipt_REJECT iptable_filter]

The entry at killefiz.de for the ipk doesn't say anything about the
modules- are they just not built in to the kernel by default?  What
would be a solution?

Thanks for any assistance.