Adding Custom fields to wp_terms table & inserting data into them

I want Custom fields like term_date_gmt & term_modified_gmt to store date of creation of category & modified date into wp_terms table, using these fields i want to extract 5 recent categories from wordpress database for Multisite,I located the code to insert category in taxonomy.php file where should i make the changes in taxonomy.php file to add these custom fields, and from where i should make changes to table to add these extra fields…

Thnx in ADVANCE….