Here is a tutorial that can help you to understand how to make mouseover in flash.
The first step to be done is setting up the work area.
First of all you need to create a new flash Document and click the button 'Modify Document'. You then have to change the background color as well as the dimension of the movie frame.
The ideal size is actually 380 x 200, because it can easily fit into a single page.
Once you have done that all you have to do is create a total of 4 layers. Each of these layers represents the number of images that you want to use.
After that you have to simply import the images. When they have been imported all you have to do is import them into a flash position.
You then select a single image and right lick on it, to convert it into a symbol. You then have to convert the image to a button and right click on it to edit in place, some button options will appear, you then have to click on the Over butter and press the F6 button to insert a key frame inside.
You then have right click on the image and choose the option that converts it into a movie. You have to use the selection tool to right click on the image again, choosing the Edit in Place option, after that you have to create a total of 3 new layers.
You then have to select the window layer and use the rectangular tool to create the rectangular shape, so as to create a background for the text. You then have to convert the rectangular shape into a movie.
Then you have to change the color to Alpha 59% and then select the text layer and write something and it is finished.
So now that you know how to make mouseover in flash, go ahead and try it.