Well actually, I think he said he wants to change the printing size, not the on-screen size. What you gave him will change both, I believe.
For some odd reason, Outlook express's font controls are controlled by internet explorer. Go to Internet Explorer/View/Text Size and make sure it is set to Medium or Small.
This problem is caused by a very recent update to Internet Explorer (update KB912812). You could uninstall the update, but that isn't probably the best way to go. For now most people are just bearing it, and hoping that Microsoft updates.
For a email client similar to Outlook, but much, much more secure, you should use Thunderbird
. It is free and will even detect your settings in Outlook and import them!