Mark,
Double-click on your Y value axis. In the Format Axis dialog box, go to
Scale. Set the maximum to 50. You can choose other options as you like (for
example minimum = 0, major unit = 10, minor unit = 2, etc.)
If you just want to show one column moving toward a goal, type the number 50
in a cell. With your curser in that cell, go to the Chart Wizard and choose
a Clustered Column chart with the Series in rows. Then, double-click on your
Y value axis and in the Format Axis dialog box, go to Scale. Set the maximum
to 50, the minimum to 0, and the major unit to 5.
Finally, to have the chart show 60% of your goal, replace the number 50 with
30.