alchymyth on "Tag Cloud with specifying font-size and category"

http://codex.wordpress.org/Function_Reference/wp_tag_cloud

try:

<?php wp_tag_cloud( array( 'smallest' => 9,'largest'=> 16, 'taxonomy' => 'category' ) ); ?>

this would show a 'category cloud' -
I don't think you can select tags from one category only;

possibly try if you can find a plugin that can do this: http://wordpress.org/extend/plugins/search.php?q=tag+cloud