You are looking for a free virtualisation solution, like VMware Player, Virtual Box and many others with a Linux virtual appliance like a Turnkey Linux.
The basic TurnKey Core Appliance is a pretty good starting point:
The common base system on top of which all TurnKey Linux appliances are built. It includes custom automated backup and migration software, a web management interface, automatic daily security updates, live installer, configuration console, and all other common features. Take a look at some screenshots.
Someone at LazyCoder has already written up a step by step guide for Getting started with node.js on Windows using VirtualBox and Turnkey Linux Core.
Personally, I would use VMWare Player, as in my experience, performance is significantly higher than the other options I mention. Now I know about it though, I might also look at using coLinux/andLinux after Jan Hudec's suggestion.