Well, if you want to give creating a drop-down menu a try, you could always just back up all of your theme files somewhere on your local computer. Then if you muck things up, you'll have your backup to fall back on.
The WordPress default theme, twenty-ten, supports drop-down menus. One idea would be to take a look in the twenty-ten style.css file and find all style rules related to the main navigation. Copy those rules over, and then paste them into your theme's style.css.
Then open the twenty-ten header.php file, and copy all code having to do with the navigation menu. Then paste those into your theme's header.php file. Make sure you enable support for wordpress nav menus in your functions.php file.
There will be adjustments to make, and you'll have to change the colors, sizing and spacing to match your theme. Lots of trial and error.
For the future, you might also want to look into installing WordPress on your personal computer. You could download XAMPP, MAMP (if you're on a Mac) or WAMP (Google them) which will set up a web server on your own computer. You can then install WordPress and test out new features like these without worrying about messing with a live site.