basic jquery/js in IE7 not working?

[BluegillMedia]

The code below works everywhere but in IE7 (and likely IE6 I suppose). Is there a way to make this code work in IE7? See below:

the js:

document.getElementById('projectDesc').setAttribute('class', 'hideDesc');

I thought there was another way with javascript to assign a class, but this was all I could find in my searching.