This is a common question. Hyper-V requires three things: processor virtualization support, BIOS virtualization support and Windows Server 2008 with Hyper-V.
Processor virtualization is provided by Intel (Intel VT) and AMD (AMD-T) processors. You can check each of these websites to see if a processor supports virtualization. AMD offers an AMD Virtualization™ Technology and Microsoft® Hyper-V™ System Compatibility Check Utility that will tell if the installed AMD CPU supports it.
BIOS virtualization support, however, can be dicey. Normally, a BIOS manufacturer will offer the ability to turn virtualization on or off -- but not always. I have a Dell Dimension E521, for example, that doesn't offer virtualization configuration. Thankfully, it's enabled by default in this BIOS.
So how do you tell if your machine will support Hyper-V? Well, the easiest way by far is to use a utility by Gibson Research called SecurAble. This handy little program will quickly tell you if your computer is 64bit, running hardware DEP and is virtulization capable.
Note that SecurAble will report that Hardware Virtualization is "No" if you run it on a Windows Server 2008 computer that has the Hyper-V role installed. This is because Hyper-V capability is "hidden" once it's installed. See the Virtual PC Guy's WebLog for more details about this.