You can find my guide for installing Koha on Windows, Mac, or Linux using a virtual machine here:
Koha Install Guide
The guide outlines two options to install. The first option is to install using a pre-made image of the Koha server. The second option is to install from scratch. So far, this guide has helped setup at least five library systems that I know about. If you find the guide useful, have a question, or a comment please send me a tweet (http://www.twitter.com/herteljt) or an email (herteljt [at] gmail [dot] com).
What brought about this Koha image? Well, a few years ago I became involved with setting up the circulation system for the small mathematics library housed in the Mathematics Department at Illinois State University. I began searching for open source Integrated Library Systems (ILS) and found that Koha is popular and continually being improved. However, I soon realized that the newest version of Koha was only available for Debian Linux and not available for Windows or Mac. Although I am a linux user, the machine I had available was running Windows. My solution was to create a virtual machine running Koha that could be used on any system. After creating the image and setting everything up, I realized it might be useful to others. The virtual machine that I created can be easily downloaded, imported, and setup within an hour or two (depending on your internet connection).