I love to have access to multiple operating systems (new and old) but I hate the fact of creating a multi-boot with 5-6 OSes, seems a bit messy and too much work for my liking. The solution, VMware Player, this allows me to run another operating system from within my main operating system.
I have Windows 7 64-bit Ultimate as my main OS and have access to other flavors of Windows 7 as well as older OSes such as Windows XP and Windows 2000 via VMware Player. I bet the first question you'll ask is how I can accomplish this with just VMware Player? The player only access virtual machines that have been created by VMware Workstation, a version of VMware you must pay for. The answer is EasyVMX.com, EasyVMX will create a complete virtual machine for you base on the OS you plan to run on it. All of this is done online and in matter of seconds you can download the virtual machine. Once the virtual machine is created, you can access it with VMware Player.
EasyVMX only create the virtual machine, no OS is installed. This is something you must do with your own license of the OS. To do this mount your OS installation CD to the virtual machine and have it boot off of that. If I mount my XP installation CD, when I start the virtual machine, it will boot into the installation CD and initialize the setup of XP and away I go. I then setup XP as if it was on any other PC. If you have more OSes, do the same and create virtual machines for those OSes.
There are functionalities differences between VMware Player and Workstation, hence one is free and the other is paid but if you are just looking for a solution to run multiple OSes, VMware Player will probably suffice.