Yellow colour pop-up box

I want to implement pop-up menu That is when some one moves over an hyperlink item, there is small yellow colour box that displays the descriptions of the particular item. For example windows applications display when we choose some item in any of the menu.
In www.yahoo.com, when some one chooses mail or finance or travel,
the cotents "mail" "travel" "finance" is displayed in a small yellow colour box near the cursor.

Please help me to implement this feature in my web design.

All you have to do is use the title attribute when dealing with links..

<a href="index.htm" title="Home page">Home</a>

This would display Home page when you rolled over the link.

EDIT: You can also employ the alt attribute when dealing with images.

<img src="image.gif" alt="description text">