[kh99]

Oh, right. If the options are 'one', 'two' and 'three' then you have to check for those strings, like

<vb:if condition="$post['field13'] == 'one'">
    One selected
<vb:elseif condition="$post['field13'] == 'two'" />
    Two selected
<vb:else />
    Something other than one or two selected
</vb:if>

Edit: also there's an elseif you can use, I changed the above to show how you'd use it.