DSi compatible sites use width tags to make the site fit the screens of the DSi using the following code:
<meta_name="viewport" content="width=240">
The number "240" represents the pixel width of the page. Sometimes, however, your page will go off of the screen. What's wrong? You simply check and be sure that any text boxes, pictures, or other items are less than 240 pixes wide.
Next part: Description.
***NOTE!!!***
Remove the underscore in the meta tag! If not, it won`t work! Just leave a space between "meta" and "name"!