This also seems to do what you want:
Code:
<style type="text/css">
div.indentlist p {
margin-left:3em;
text-indent:-3em;
}
span.label {
display:inline-block;
width:3em;
text-indent:0;}
</style>
</head>
<body>
<div class="indentlist">
<p><span class="label">One:</span>The quick brown fox jumps over the lazy dog is an example of an english sentence with all the letters of the alphabet.BTW, to get this text nicely aligned, you should not have a space after </span></p>
<p><span class="label">Two:</span>The Sahara desert contains enough sand to cover almost all of northern Africa. If you put all the salmon fished in Alaska during one season along Route 66, the stink would be simply awful.</p>
</div>