Quick answer is VirtualBox. Free for personal use, and there is a GPL version. I’m trying out the PUEL version (free to check it out, free for personal use, not free for commercial use ($50)).
Step 1. Download and install the linux host. I’m using 64bit CentOS, linux
http://www.virtualbox.org/wiki/Downloads, and the final download location was http://download.virtualbox.org/virtualbox/3.1.4/VirtualBox-3.1-3.1.4_57640_rhel5-1.x86_64.rpm.
next add your users to the vboxusers group. Wow, seems to be no easy one liner to do that (normally just edit /etc/group). Usermod doesn’t take a group name (only the id), so here is a quick hack for you (group “vboxusers” exists after rpm installation above):
Suggest you just edit /etc/group :).
Now run Applications -> System Tools -> Sun VirtualBox
Enter in a name (I used “windows7”), enter in the Version type (I’m using “Windows 7 (64 bit)”) and hit Next.
Now you need to choose the amount of memory. My machine has 6gig on it, and a quick look on top shows that I’m “only” using 2g. So I set the size to 3gig. My thinking here is that if I have the VM running, I want it to run well, if I need the memory back, I’ll shut down the VM. Click Next.
Now we need to choose a virtual hard disk. I googled around a little to see if I could my existing install, but that doesn’t really seem to be possible. Some information is here: http://www.virtualbox.org/wiki/Migrate_Windows
Enter your product key. I’m using the one that is already installed on the box. We’ll see how that goes!
Well that went surprisingly well… It’s a shame that you can’t have it run off the same install that I already have (like I will do on my macbook), and perhaps this is not the end of the licensing story.