Mobipocket Reader is a fully featured reader for the desktop. It reads a variety of formats, including the mobipocket .prc format.
To install it, download the msi installer file, and run from the command line, msiexec /i mobireadersetup.msi. You may need to install additional software for this to work (DCOM98, Internet Explorer, and Microsoft Office are installed in my Wine directory). Please post if you have to install other files to make this work