Boot with u r first Mandrake cd and at the boot prompt type
"linux askmethod" with out quotes.
then u have to specify how to continue with u r installation further.since
the installation images are in D:\ drive it will be /dev/hda5 if u r hdd is IDE Make sure that u keep iso images in "D:\" but not in "D:\mandrake9.1\...."
Hope this helps