John,
I'm not sure why you would have a problem at that particular resolution, but
most folks will recommend getting rid of the hover buttons completely.
Those hover buttons require that a Java Virtual Machine (JVM) be installed
on the visitor's computer. Due to some disagreements between Sun and
Microsoft, many computers with Windows XP do not have a JVM at all. This
means that those folks can't see your buttons and the links don't work. All
they get are plain gray boxes in the spots where your buttons should be.
Basically, your site can't be used in this instance.
If you insist on having a rollover style on your links, consider using
JavaScript. JavaScript is part of the browser and doesn't require any
external applications be installed. Really, the only thing that JavaScript
has in common with Java is the name.
Here's a code generator that can get you started with the rollovers.
http://javascript.internet.com/generators/preload-images.html
Good luck!