The VMAfter a little bit of playing around, I managed to settle on Ubuntu 13.10 running under VirtualBox. Unity is the default window manager for Ubuntu, and is a little heavy for a VM, but it runs ok. The host is Windows 8.1 which is my preferred desktop. I've tried Linux as a desktop OS in the past and I always found reasons to go back to Windows (such as Steam, and RAW handling for my Canon). I'm used to working on servers running Windows Server, but I don't have to pay for them, so Linux is a nice alternative to get used to, especially for web development, which is outside of my normal experience.
NetworkingThe main thing I wanted working was networking. The VM needed to reach the internet in order to download new packages etc, and I needed to access the VM from Windows. Accessing the Windows host from the Ubuntu guest was less important, but I got that working too.
The default network adapter is a NAT setup. This allows access to the outside world, but there is no connection between the guest and the host. The first promising one was the Bridge network. I could access the VM from my Windows PC, but the VM couldn't access the host or the Internet. Luckily a reboot of the VM fixed that. Bridge networking now gives me host to guest, guest to host and guest to Internet.