Windows 7 is an operating system
Workstation is another name for the desktop computer/desk your working at. I also belive workstation is the name of some software by VMWare which is basically virtual machines (machines that run off a server).
Editions of Windows 7 are:
Windows Home Premium
Windows Home Premium N
and then theres 32-bit or 64-bit versions of each. http://windows.microsoft.com/en-GB/windows7/products/compare