Mike is using Serif Web Plus so the way he does it might not work in
Publisher.

There are several ways you can do it with Publisher. Assuming that you don't
want to import your smaller images along with the code that would open a
window with the larger image, then you can apply the link to the smaller
image using the hotspot hyperlink.

Reference:
http://office.microsoft.com/en-us/publisher/HA011587451033.aspx

The first javascript code snippet is incorrect on the website. Use this
instead:

<script language="JavaScript" type="text/javascript">function Show(Url,
Name, Features) { window.open(Url, Name, Features); }</script>

Once you insert that into your page via the code fragment tool, you can
build your hyperlink. Click the Hotspot icon, and copy and paste the
following in the address:

javascript:Show('http://www.breladecockerspaniels.co.uk/images/cocker_spaniel_dogs/morg1.jpg','ne
wwindow','')

Move the hotspot over the small image, and resize it accordingly. Do a web
page preview and click the image, and it should open "morg1.jpg' in a new
window.

Go back to the reference page and add the attributes you want to the basic
code snippet I provided to get a window sized and formatted as you prefer. I
would suggest building your links in NotePad or a separate text box in the
scratch area using Courier font. You are less likely to make errors than if
you try to edit the code in the address field of the hyperlink dialog.

DavidF