In my case I've got lucid installed on my server but want to install a newer saned version.
There is one in the maverick and lucid repositories, how would I add this repository for just that one package?
What should I look for when doing this?
SnapOverflow
In general you can't mix packages from different releases. It may work in some cases when the dependency changes do not have an impact on the package upgrade.
Your options are to either find a ppa which provides an updated version for your release, or rebuild the package yourself from the latest source, you can find how to do this at: http://www.cyberciti.biz/faq/rebuilding-ubuntu-debian-linux-binary-package/