If you are a reseller, even someone who sells PCs on a part-time basis, you will want to learn this neat little trick because it can save you time setting up different systems, partitioning and formatting hard drive with Diskpart, backing up hard drive using ImageX, connecting to network, troubleshooting using Windows-based programs, system recovery and many more.
"Windows Preinstallation Environment (WinPE) is a lightweight version of Windows XP or Windows Server 2003 or Windows Vista. It is used for the deployment of workstations and servers by large corporations. WinPE 2.0 is actually the lightweight version of Windows Vista with minimal GUI and drivers, with the ability to detect USB drives on-the-fly. Just plug it in, run diskpart and then list vol. You should see your USB drive listed with drive letter assigned."
Check it out at TechARP.