Looks like he meant output of the guestbook which seems to be font size 5 or so.
Just change font size in the script. So if you look at the scrip in .txt extention instead of usual .pl there should be an string that says something about font size even in perl language.
So basically if you own the domain acess your cgi bin, save your guestbook script, rename it to (whatever).txt look for font size, then change font size, save it and rename it to previos extention then upload it back to your site. (might want to save a backup copy before you mess with this tho)

Email me if this is not what your were looking for, i should be able to help ya either way.
Hope this helps.