You can modify the font type colour etc to give better contrast with your desktop. Since this won't need updating that often set the refresh to 5000. Now type cal in the box and in a few seconds the calendar for the current month should appear on your desktop at the top left corner. To create a new entry click the button at the bottom left and then select 'Shell' from the dropdown menu. You can now access it by opening System Preferences and looking in the bottom row of icons, double click it. To install GeekTool go to the website, download it and double click to install the preference pane. In this tutorial I'll use a couple of simple commands to create desktop content, and then link to Applescripts to create more complex content.
I first became aware of Geektool when read this tip on Macosxtips and it would certainly be worth looking at to get an idea of what it can be used for. The information can be derived from a shell script or using osascript it is possible to call applescripts (or any other OSA language scripts). It lets you display various types of information directly on you desktop. GeekTool is a Preference Pane (System Preferences module) for Mac OS X.
