The book I read to research this post was VMware Vsphere For Dummies by Tom Keegan et al which is an excellent book which I bought from kindle. Vsphere is a virtualization operating system used on networks which because you enter what is known as a virtual machine that only has predefined functions any virus or other malware that infects your computer is severely limited in the damage it can cause. Most viruses are written specifically to infect Windows operating systems so any other operating system limits the vulnerabilities. A Vsphere package normally comes with a client version, a server version & EXL version. These run on the workstation and server respectively. There are 3 main versions which are v3.5, v4 & v4.1 with the latter being the newest. Also there are several versions and 2 of them are for small businesses and the rest are for big companies. They use a proprietary file system called VMFS or Virtual Machine File System. It's compatible with Oracle & Microsoft SQL Server. If you use a demo of SQL or the Express version it only works with a database upto 4GB. Also the latest versions only work with 64 bit processors. In terms of your hardware limits you are much more likely to be limited by your network hardware than be limited by what Vsphere supports. The latest version works with upto 8 processors for example and these can each be subdivided to up to 8 virtual processors. Virtual processors though can slow down your overall performance. There is a website at
http://vmware.com which lists the requirements for your network and what is compatible. It's essential to plan your network prior to installing Vsphere.