help needed : create tag mod ...

hello dear friends ...

I need to create the tag mod for forums ...

when a user post a topic, he can enter some keywords/tags for his topic.

for example this topic tags are :  webwiz, forum, mod, asp, tag, help

and create a page (tags.asp) too list most used tags ...

just like this :  http://www.fanhome.com/forums/tags.php

and the font size of important tags is bigger than others ...

but my problem is this :
i crate a column in topic table named : "tags" and user insert  tag1, tag2, tag3, tag4, ... in this column .
but how I can count used tags in this column to find important and most used tags ???  


and I suggest to add tag system to version 10 ...