If you're using CSS to specify the font face, and you should be, you should always specify several fonts at once and you can specify different font's for every page element, id or class. For example, the <body>, <p>, <h1>, <td>, <div>, the list goes on.
This way, if the user does not have the first specified font installed, the browser will default to the next system font in the list.
Here's how:
(In your CSS stylesheet)
HTML Code:
body{font:76% arial,helvetica,verdana; color:#000;}
Alternatively, you can apply different styles to each element like this:
HTML Code:
div#content {
font-family:arial, helvetica, verdana, tahoma;
color:#D2D5D8;
font-size:1.3em;
font-weight:normal;
p {font-family: "Courier New", Courier, monospace; }
As you can see, you have a lot of flexibility. A word to the wise though, try never to specify comic-sans, script or brush fonts that your users probably won't have installed and that are difficult to read anyway.
For more information regarding CSS Styles, visit the W3C page at:
CSS Tutorial
Enjoy!