How can I make a category graph -- a XY plot with a categorical X variable?

Prism 4 offers the direct ability to make category graphs. Simply pick this option from the two-grouping variable graph options in the Welcome screen.

With Prism 3, you can make category graph in the following way. Make an XY graph, using numbers to code your categories (the particular values of the numbers will control horizontal spacing between categories). Now double-click on the X-axis and, from the "Format Axes" dialog, click "Custom Ticks". Now you can tell Prism to place any text anywhere on the axis and whether to include ticks or grid lines.