Easiest way to accomplish that should be mounting the install.wim with imagex.exe. Changeinto \WINDOWS\SETUP in your mountpoint and create the directory "Scripts". Place a .cmd file there called setupcomplete.cmd and call WPI from there. Be careful with the old CD-ROM/DVD-ROM detection code that looks for WIN51IP though, accessing a none-existant device in Vista results in a error messagebox that halts the install process. I might have the workaround I used somewhere still. If I remember correctly I checked with the "vol" command if a drive-letter is a valid volume by processing the errorcode that vol returned... Or add WPI to a directory in the install.wim and thenn call it with %PROGRAMFILES%\WPI\WPI.EXE or something like that