In some situations, you might need multiple computers, so you'll just need to get a new keyboard, mouse, and display each time, right? Instead, try a more effective--and cost-effective--ways to use two systems. Here area few ways to get multiple-system benefits without the full multiple-system cost.
If you just need to check web design within different versions of Windows, for example, you could run those operating systems in virtual machines. In this case, you'd just use a single computer, but the VM software allocates your hardware resources so that you can install another operating system at the same time.
VMware Workstation is one way to create that virtual machine. You'll need to provide your own OS installations for each virtual system. Once set up, you can toggle between the two operating systems, or even use them at the same time. Virtual machines are great for general use, however, for tasks with high-end system requirements, such as video rendering or gaming, they'll be noticeably slower than a dedicated PC.
Share a keyboard, display, and mouse
A simple KVM (keyboard, video, mouse) switch can toggle those devices between several PCs. An IT department might connect several PCs to a single monitor, keyboard, and mouse, for example. These switches are usually reliable, although they're not as interesting as the following options.
Enable remote access and VNC
Instead of using a physical switch to trade screens and input devices, a virtual network computer (or remote access) connection lets you control a remote PC within your current system. Like a virtual machine, you'll notice slower performance, since significant data has to flow through your network. But unlike a virtual machine or KVM option, you can control PCs anywhere within your office--or throughout the world
Bridge input devices between systems
If you need to run two side-by-side systems with their own displays, you can use the same keyboard and mouse. You'll save money on a second keyboard and mouse, but the biggest benefit saves the hassle of constantly moving between two sets of devices.
Try Input Director to control multiple PCs, Teleport, to control multiple Macs, or Synergy to control both. You'll install the utility, then when you want to swap to the other system, you'll just move the mouse between the displays. It's a slick trick that outlasts its initial showmanship.
Based in San Francisco, Zack Stern frequently contributes to PC World.