Maybe you're experimenting with git and bzr and you think svn is oldschool. Maybe you don't know what any of those words mean. All the same, if you need Subversion 1.6 on an Ubuntu Hardy machine here's the steps I followed to get it working:
1. Get the sources set up for an alternate svn repository
I used Anders Kaseorg which seems to be fairly popular.
Add these two lines to your /etc/apt/sources.list:
2. Get Anders key:
sudo apt-key adv --keyserver keyserver.ubuntu.com --recv-keys 413576CB
3. Update/Upgrade
sudo apt-get update
sudo apt-get upgrade
Glory!