Admin Notes is a small plugin that allows you to create and manage a very simple notes system for maintaining a to-do list etc.
Once activated Admin Notes will appear under your WordPress management options. Simply enter any notes in the text box and press the update button. Notes are displayed on your dashboard.
Simply download the Zip-Archive and extract all files into your wp-content/plugins/ directory. Then go into your WordPress administration page, click on Plugins and activate it.