Let's take a look at how you can take advantage of this feature in Fireworks CS3.
First, go to the Edit Menu and click on Insert and choose New Symbol. Make sure you click the check box to Enable 9-Slice Guides in the following options box.
This is what the 9-Slice Symbol window looks like -
Next, let's add a graphic element to the symbol. Select the Rounded Rectangle Auto Shape from the Tools palette.
With the Rounded Rectangle Shape selected draw a rectangle in the symbol window and make sure the edges of the rectangle are within the boundaries of the 9-slice guides. Here's what that should look like -
To add some flair to the symbol, select the symbol and click one of the styles from the Styles palette.
In this case, I used the Dark Chrome style.
Now your symbol will look like this -
Next, return to the main canvas/stage window and select the Text tool and add some text to the shape
Now, you can make some copies of the symbol, modify the text on it and use the scale tool to make the symbol fit horizontally with the text without distorting it's corner radius.
Have Fun!
