I have installed Acad 2004 y Acad 2006. A u t o P L A N T__X M works fine in both, but in Acad2006 shows some messages at beginning (although they are not errors) and project preferences are not accessible from piping module (I access from equipment module)
My OS is Windows XP SP3 and also I have installed A u t o P l a n t 2004.