Virtual Server 2005 is a free software from Microsoft. You can download the Virtual Server 2005 R2 - Enterprise Edition from Microsoft web site. Follow the below link to download Virtual Server:
Even though it is a free download, you must register to download this software. Follow the instructions on above page to continue with registration. You must provide your name, email address and some other details to complete registration. After you finish registration, you will get the link to download the software.
The download page will probably show 2 links:
32-bit X86 Executable
If you are using a 32 bit operating system as host computer, you may want to choose the 32-bit X86 Executable link.
The setup.exe is around 28 MB. Download it to your machine.
The installation is very straight forward. Follow the setup wizard and complete the process just like any other windows installation.