SurfinBird

Hello, I have WinPE images on SBS 2003 RIS server, all working perfectly unattended except there is one annoying little thing I have not yet figured out. I don't want all clients to create computer account in AD and solution was found at Microsoft Business Desktop Deployment page. However this does not work. As I change ImageType from Flat to WinPE, .SIF I was editing disappears from clients options. Anyone have a solution?