Hi Dave,
starting with Outlook 2007, Word is used as rendering engine for HTML messages, causing a lot of problems with margins and alignments, which are just ignored in some cases.
I would suggest that you use a table with one row and three columns and then put one IMG tag into each cell, like this:
<table>
<tr>
<td style="width: 100px">
<img alt="" src="images/square-logo-for-Nursery.jpg" />
</td>
<td style="width: 100px">
<img alt="" src="images/OutstandingLogo1.jpg" />
</td>
<td>
<img alt="" src="images/NW2010.jpg" />
</td>
</tr>
</table>
The default vertical alignment mode is 'middle', so no overwrite is needed.
The width of the cell (to introduce some space between the images) is specified by 'style="width: 100px"'. You may need to use another value, depending on the width of the pictures and of the space desired between them.
-Franz