You'll want to use CSS.
Or just HTML for that matter, but many will hound you about it.
CODE
.class { font-size:9px; }
That would make text with the class set at the name class to 9 pixels.
CODE
<span class='class'>This is 9 pixel text</span>
You can also use 'pt', which most recommend.
.class can be whatever name you want, as long as it doesn't conflict with something else.
Chad