You'd need to leave them as inline elements and then you can align them to the baseline as required.
Code:
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
<head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
<title>Untitled Document</title>
<style type="text/css">
body {
font-size:200px;
}
#one {
font-family:garamond;
vertical-align:baseline;
}
#two {
font-family:verdana;
vertical-align:baseline;
}
</style>
</head>
<body>
<div><span id="one">a </span> <span id="two">a</span> </div>
</body>
</html>
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