The way I test software is to create multiple virtual machines with different OS and then installed the required software. Seems like you want to do the same.
I usually use VMPlayer (free download) to create virtual machines. In case you do not have the required OS's you can download trial versions of Windows 7 (90 days) and Windows 2008 Server R2 (180 days) as OS's for the virtual machines. The trial versions are available either in Microsoft websites or other Tech sites. Creating VHDs with VMWare player is as simple as clicking a couple of 'Next' and 'Finish' buttons
You should be able to get the OS's for Vista and XP as well from the internet to set up their respective virtual machines. In case you already have a CD or DVD with the OS's, VM player will be able to read the CD/DVD players to help create the virtual machines.