[Dismounted]

<if condition="$post[fieldx] === '2'">
<img src="$post[field1].gif" border="0" alt="" />
</if>
<if condition="$post[fieldx] === '3'">
<img src="$post[field2].gif" border="0" alt="" />
</if>

Change x in $post[fieldx] to the menu field id.
Change the 1 & 2 in $post[field1] & $post[field2] to the field numbers.