Getting those virtual machines up and running doesn't necessarily require that you invest in new server hardware. If the existing system you have in mind is of a recent vintage, you might be sitting on an ideal candidate .

Ken Hess discusses how to identify them in his "First Steps to Virtual Enlightenment" article over at the main site.

If you’re thinking of using existing hardware as a virtual machine host or hypervisor, you’ll have to make sure that the hardware is capable of supporting the virtualization software and virtual machines. Newer multi-core, 64-bit Intel and AMD CPUs have built-in virtualization extensions to support the extra load. At a minimum, your potential host systems must be 64-bit, dual-core and preferably quad-core or higher.

The quickest method of discovering your systems’ virtualization potential is to reboot and enter the BIOS settings. Once you’ve entered the system’s BIOS, look for Virtualization, VT, EM64T, AMD-V or SVM. Enable the virtualization extensions and power off the system and power it back on for the change to take effect. Your system documentation also provides information on these extensions or find it online at your vendor’s website.

At the very least, it's worth invoking the BIOS configuration screen during the next reboot. Don't know how to access your BIOS? Read this About.com article for some good rules of thumb.