How do you alert users without refreshing the page

I have created a PHP script that checks to see if the new users username is already in the database, but I can't figure out how to alert the user about this without refreshing the page so the user loses all her imput. How do I alert the user without losing all the form data. (I thought I cout use div tags or mabye something with javascript but I'm not sure.)

Thanks in advance!

~Imozeb

 

One word: AJAX

 

Either use Ajax, or just re-draw the form with the user-submitted values pre-populated (<input name="age" value="97">).

 

Thanks everyone.