You can get the official Plug-and-Play documentation from the Microsoft ftp site. These documents are .EXE (self extracting) MS-Word format files. The documents are the industry (MS) specifications for PNP on BIOS, SCSI, Peripherals, etc.
Craig Hart also has a good page on PNP programming at http://redir.no-ip.org/mirrors/members.datafast.net.au/dft0802/ (mirror of http://members.datafast.net.au/dft0802/ )
You could also check out http://linux-sxs.org/programming/interfac.html