To generate a contour plot in Minitab, I first had to read the 
data file power.dat.  To read the file, select File>Open Worksheet...
and scroll down to "Text" under "List Files of Type..."  Choose the 
appropriate directory and make sure power.dat is listed as a text
file (if not, you may have to type it in).  Before pressing OK, 
select Options and under "Variable Names", select "None". Click
OK to clear both screens and the file should be entered correctly.

To produce the contour plot, select Graph>Contour Plot and enter
values for the Z, Y and X columns (the choices for Y and X are
essentially interchangeable--be sure to choose the power for Z).
Under "Options...", click the "Values" button and then enter a
set of evenly spaced values in the dialog box (I usually choose
.70 .75 .80 .90 .95).  You can also enter the values in a column
and select that column number for the dialog box.