[This method also works for Kubuntu 8.04 64 bit and Flock 1.1 - see the update at the end of this post]

This turned out to be easier than I thought! First you need to get the deb file from getdeb.net and install it manually it manually:
sudo dpkg -i flock_1.0-5~getdeb1_amd64.deb

This will set up Flock on your system and create the appropriate menu entries.
Next job is to get Flash installed. Flock is actually a 32bit application but runs on 64bit, so it understands 32bit plugins (I think that is right) so no need to worry about using something like nspluginwrapper to create a 64bit plugin for us

Wow! From the look of this thing you would be forgiven for thinking the Kubuntu team have spent six months spitting and polishing this fine operating system to make it a really smooth user experience. I have just installed the 64bit version onto my aging Acer laptop and it has taken remarkably little time to get everything up and running.