help with banners in my navbar

[JamesUK]

Hi guys,
I'm trying to put some subtle banners into my navbar and I'm half way there, but I'm struggling a bit with the technical side of things

This is a mockup of what I'm trying to achieve:


2 separate images, both randomly selected from a possible 15 or so, one will be an ad banner, the other smaller one will just be a filler to make things look consistant.

so far, I've just inserted the following code in the navbar template

<div align="center">
<img src="path to my image.jpg" />
</div>

after

<td class="alt1" width="100%">
<if condition="is_array($navbits)">
<table cellpadding="0" cellspacing="0" border="0">
<tr valign="bottom">

and

<if condition="$show['member']">
<td class="alt2" valign="top" nowrap="nowrap">

and

<td class="alt2" nowrap="nowrap" style="padding:0px">
<div valign="top" align="center">

This is very close to the desired result, but just not quite right......

I get this when people are logged in:

the two images don't quite line up at the top. The right hand one is higher...

and this when they are logged out:

where the right hand image spills up over the top, really messy.....

Once I have the pics sat in the right place, I can swap the image code for some that pulls a random image from a folder, once I work out how to do that......

Does anyone have any pointers for where I'm going wrong?
Should I be creating some more table elements and putting these pics inside them or something?

thanks
James