It boils down to whether the CPU in your machine has the the VT bit (Virtualization), and the BIOS enables you to turn it on. For instance, my laptop is a Core 2 Duo which is capable of using this. However, my BIOS doesn't enable me to turn it on.
Note that I've read that turning on this feature can slow normal operations down by 10-12%, which is why it's normally turned off.