Everybody can download VMWare Server for free from
VMWare Server download page (discontinued). However, to install VMWare Server, users need to have serial number or product key, which is also available for free. From the download page, the Download button is so prominent that you might easily miss out the register link that is where you can get the free serial number(s), as the Download link will not provide any keys to install VMWare Server other than allows you to download the installer setup file.
So to get VMWare Server free serial number or product key, simply complete registration at
http://register.vmware.com/content/registration.html (obsolete). You can get for free up to 100 serial numbers at one go without any charges or fees.