Those of you that have ever been involved in project management should be very familiar with Gantt charts. If not, I think it'd be good for you to learn what they are. GanttChart.com states that it's a "graphical representation of the duration of tasks against the progression of time." Gantt charts are incredible useful for graphing project schedules because you're able to glean a lot of information from them in a short amount of time. GanttChart.com has a lot of useful resources on Gantt charts, including the history of them and some examples.
Most project management application (like Microsoft Project) come with the ability to create Gantt charts easier from one click after you've mapped out your project schedule. However, when you add all of the other bells and whistles needed to do complete project management, this software is very expensive; and if you don't need the other features, why spend thousands of dollars just to generate Gantt charts?
This is where Microsoft Excel comes in. Jon Peltier has written an article demonstrates two methods for creating Gantt charts: Worksheet Formatting and Stacked Bar Charts. Worksheet Formatting method involves shading the appropriate cells to show when tasks are assigned to be done. You can either shade the cells yourself, or use conditional formatting to do the work for you. The Stacked Bar chart method, however, will give you a chart that is more professional-looking and versatile to do other things with.
For even more information, check out Jon Peltier's web page that lists other links on creating Gantt Chart using Microsoft Excel. This page also lists other tools that you can use to create them for FREE.