Out of the Microsoft Office Products, Visio can also do Gantt charts.
IMO, if all you're after is a gantt chart, then customization-wise, Excel has the least, Project in the middle, Visio is the most customizable.
From my brief search online, it seems Excel creates Gantt charts through what is essentially a Bar Graph. Depending on how savvy you are, you can create many functions you can find in Project. (The immediate exception appears to be showing the linkage between tasks, showing Summary Tasks, or Milestones differently from other tasks).
Microsoft Visio's focus is charts, graphs and diagrams. The Gantt Chart Wizard in 2003 seems pretty neat, allows you to link tasks, and show summary tasks and milestones as different symbols from the other tasks. You can do a whole lot of crazy things visually as it's focus is ultimately the picture.
Microsoft Project is a collection of project management tools. Above the other two, it can be used to define and measure costs. It can be used for managing resources, task assignments, and can be used to store and track against baselines. It can more easily (IMO) be used to manage a project, as the functionality is there (in excel you have to create the functionality yourself). The downside being a steeper learning curve. It's not like Microsoft Word or Excel that you can just pick up and start using. (I've seen accountants use excel to enter numbers, then use a calculator to sum it up, and place the number in the last cell.)
In summary, depends on your budget and scope. If you want to just create a one-off Gantt chart - stick with Excel. If you want to have multiple capabilities in one tool, and have the money to pay for training (or a good book) and the product, Project is good.
Ultimately the tool you choose comes down to what you feel comfortable with. I'd suggest taking a Project course, or read through a book on it, and see if you feel Project's other features will be useful to you. Choose the tool that makes you more efficient