Virtualization

a quick and good starter would be the wikipedia for the theory.

Then if you know which solution you want to have do the trainings of the vendors. The major vendors have some stuff free (like Vmware University to get the VSP and VTSP) and other stuff will cost.
On their pages you will find also many informations in the KB

I would highly recommend contacting a vendor who can guide you through the process. They can educate you on how it works, your options, hardware requirements, and transitioning existing machines over to the virtual environment. You must take numerous things into consideration when virtualizing such as storage, networking, server hardware, backups, etc that can not be answered without knowing your environment, your reason for virtualizing, budgets, etc.

That is a very broad question.  What are you intending to virtualize?  File servers?

What do you want to virtualize?

Application?

Desktop?

Server?

etc..

If you are looking for application virtulization you can go through below links.

http://technet.microsoft.com/en-us/library/jj680850.aspx

http://www.microsoft.com/en-us/download/details.aspx?id=27760