In an ideal world you’d achieve this simply using the following css
<style type="text/css">
span {
display: inline-block;
width: 50px;
}
</style>
This works on all browsers apart from FF2 and below.
Firefox 2 and lower don’t support this
value. You can use -moz-inline-box,
but be aware that it’s not the same as
inline-block, and it may not work as
you expect in some situations.
Quote taken from quirksmode