Joomla 1.5

[plainjane]

I would like to know if and how to install joomla 1.5.

[troycawley]

The fact that you are asking how to install it leads me to assume you probably should not install it.
Do you have an existing (outdated) installation of joomla? What kind of site are you going to use it for?
But if you want to learn how to install it:
http://downloads.joomlacode.org/docmanfileversion/1/7/4/17471/1.5_Installation_Manual_version_0.5.pdf