Uma explicação simples

http://www.microsoft.com/windows/virtual-pc/support/configure-bios.aspx

Verificando se seu processador AMD da suporte a virtualização por habrdware

AMD Virtualization Compatibility Check Utility

Verificando se seu processador Intel da suporte a virtualização por hardware

Intel Processor Identification Utility

Sample instructions for your PC 

Dell systems

• Depress the F12 key when boot menu text appears at startup

• Select BIOS setup and depress the Enter key

• Using the mouse, expand the Virtualization Support menu item by clicking on the plus to the left of Virtualization Support and select Virtualization

• Check the Enable Intel Virtualization Technology checkbox

• Click Apply

• Click Exit

• Fully shut down (power off), wait a few seconds, and restart your computer

• Depress Esc key when prompted at startup

• Depress the F10 key to Configure BIOS

• Scroll to System Configuration using the arrow keys

• Select Virtualization Technology and depress the Enter key

• Select Enabled and depress the Enter key

• Depress the F10 key to save and exit

• Select Yes and depress the Enter key

• Fully shut down (power off), wait a few seconds, and restart your computer

• Depress the blue ThinkVantage key when prompted at startup

• Depress the F1 key to enter the BIOS setup utility

• Using the arrow keys, scroll to Config and depress the Enter key

• Scroll to CPU and depress the Enter key

• Scroll to Intel ® Virtualization Technology and depress the Enter key

• Select Enabled and depress the Enter key

• Depress Enter key to continue

• Depress F10 key to save and exit

• Select Yes and depress the Enter key

• Fully shut down (power off), wait a few seconds, and restart your computer