Way to display sub categories only

i would like to display sub categories only .

i have three main categories and each category have around 500 – 1000 sub categories

would like to display each category >> sub categories in a page with three columns arranged alphabetically ( only sub categories not the category)

if we are using the shortcode [CATEGORIES SHOW=”456″ COUNT=”1″] we are getting the category also which i donot want.

can anyone share the php code / shortcode or guide me in the proper direction.

thanks
kiran