I purchased Parallels for my (January 2006) 20" Mac Pro Core Duo 2.0GHz, but I'd like to move it to my Mac Pro 3.0 GHz Quad Xeon. I'm assuming the Parallels license allows this if I uninstall the copy on the iMac?
You should be OK I do not think you need to do anything special. The guys at Parallels allow you to move the copy to another computer without having to deauthorize the software. So you can have the software on multile machines and It is a trsut issue, and if you think you are using two copies at the same time I would buy another copy, but if you use one copy at a time, I think you should be OK.
The iMac is my work "PC" running Windows XP nearly full-time, so I don't really need Parallels on it. I don't intend to use Boot Camp on my Mac Pro, but would like Parallels on it for my Linux software development work. I would never need to run Parallels on both machines at the same time, and in fact will never need Parallels on the iMac at all now that I have the Mac Pro.