UPDATE:
I started with kernel 2.6.35.4 #2 and lsmod | grep ipt = ipt_LOG 5419 2.
My service provider produced a replacement kernel 2.6.24-28-xen #1.
Now lsmod | grep ipt reveals ......
ipt_LOG 8192 2 iptable_filter 4608 1 ip_tables 24232 1 iptable_filter x_tables 23432 5 xt_string,ipt_LOG,xt_state,xt_tcpudp,ip_tables
and, to my personal joy and pleasure,
iptables -A XXXX -p tcp -m string --algo bm --string 'login' -j DROP
is accepted by IP Tables.
Thank you to everyone who contributed to this thread.
With best regards,
Paul.