I required the module connlimit to limit the number of connections on one of our Debian firewall boxes. First download the iptables-1.4.2.tar.bz2version from Netfilter.
Unpack the tarball
tar -xjvf iptables-1.4.2.tar.bz2
if you just use ./configure then everything will be installed to /usr/local
make and install iptables
After that you can check your new iptables version
The only problem i encountered is apps which need iptables as dependency beacuse aptitude will try and install the old version of iptables again as a dependency. Either you install those apps from source as well. Or you can install two versions of iptables one under /usr/local and one under /sbin which can be confusing.