CSS image in <ul> for Outlook?

[LLLL]

I'm trying to use CSS to bring an image ("bullet.gif") in as a bullet for each <li> element, and have this image show up when the HTML Email is viewed in Outlook 2007 when sent through OpenEmm.

So far, the bullet.gif image I'm using isn't showing up in Outlook, but IS showing up in Yahoo. I'm loading the bullet.gif image as usual when I do my test email in OpenEmm.

Here's how I defined the <ul>:

ul {
list-style-type: none;
padding: 10px;
margin: 0px;
}

li {
background-image: url([agnIMAGE name=bullet.gif]);
background-repeat: no-repeat;
background-position: 0px;
padding-left: 18px;
padding-bottom: 10px;
font: 12px Helvetica, Arial, sans-serif;
color: #666;
}

And here's how I call it in:
<ul>
<li>Employ timely, relevant strategies and ground breaking ideas gained from in-depth sessions hosted by recognized industry leaders.</li>
</ul>

Help?