Sun Virtual box is free but limited and a bit clunky compared to VMWare:
Here's the site for VMWare:
VMware Virtualization Technology, Virtual Machine, Green IT Servers, Hypervisor - VMware
Essentially it's best to have VMWare Workstation to set up your VM. If you are friendly with the IT people where you work then ask them about it. They'll probably already know about the program. You'll need to install VMWare Tools after you have the VM going... it makes it seamless for your mouse to go from your host computer to the VM, and to do things like drag and drop/copy files off of the VM to the host machine and vice/versa.
Virtual Machines are the shit, yo.