Start with the dependencies:

apt-get install zip unzip ipset

Then add this to your existing iptables firewall script:

ipset create sfs_block hash:net
iptables -I FORWARD -p tcp --dport 80:443 -m set --match-set sfs_block src -j DROP

Then a script that updates the ipset:

ipset destroy tempset
ipset create tempset hash:net
cd /tmp
wget -N http://www.stopforumspam.com/downloads/listed_ip_7.zip
unzip listed_ip_7.zip
sed 's:^:add tempset :' listed_ip_7.txt > listed_ip_7_importfile.txt
ipset restore < listed_ip_7_importfile.txt
rm listed_ip_7_importfile.txt
ipset swap tempset sfs_block