I've manually installed the 18.104.22.168 kernel, added an extra entry to my Grub menu.lst and I'm currently using it. Seems to be working fine (though no madwif drivers). After the first boot I ran 'depmod -A' as root and rebooted.
I'm getting a 'failed' message on 'setting up modules', though all the modules seem to be loaded. I can't see a problem, but I'm curious as to what could cause the error message. Can't see anything in either dmesg or syslog, so I'm not sure where else to look?
I'll try the other alternative later. In the meantime, I may see if my package building skills are up to building the madwifi drivers.