There are two virtualization technologies on our processors, the first is VT-x which is the standard virtualization on a Window 7 system it will allow me to run Window XP virtualization.
The other technology is called VT-d and this allows virtualization with directed I/O. This gives you the ability to assign hardward to an VM. So let say I am running a VM and I want to give it access to the network I can assign a LAN port to it (this is just one example of the difference.
Intel® Core™ i5-3570K has VT-x but not the VT-d. The Intel Core i5-3570 has both but you also need to have a board that support VT-d.
You can see the differences between the Intel Core i5-3570 and the Intel Core i5-3570K at http://ark.intel.com/compare/65702,65520