Recent versions of Makefile.PL automatically locate the ImageMagick installation using IM's "identify" command. That will only work if IM is in your path (which is an installation option). Check like this:

C:\>path
PATH=C:\Program Files\ImageMagick;C:\bin;...
[download]

You will also need to replace "-lMagickCore-6.Q16" with "-lMagickCore" in Makefile.PL and comment out the RadialBlur case in Magick.xs, as described in http://www.imagemagick.org/discourse-server/viewtopic.php?f=7&t=25746&p=113771#p113771.