WinPE and BartPE are both preinstallation environment - they are designed to start windows installation from network. They provide you with basic tools of Windows XP/2003, like native APIs or WSH support. You can work around MOST of their abilities using dos, but a.) it is designed for future, I mean changes will be made to them instead of dos (for example WMI support in WinPE 2004). So if you are beginning with network installation, it is better to use them instead of creating dos boot medium. You can also began with installation without restart, which is impossible in dos (you need to create install partition, restart and run installation) b.) it is much easier to create scripts in WinPE than in dos environment.