In Drupal 6, you can get the term object using the following function
taxonomy_get_term($tid);
In Druapl 7, this function is deprecated but you can get the term by term name.
taxonomy_get_term_by_name($name);
If you want to get the term by term ID, there is not yet a official solution but hopefully you could find more information in the following discussions.
Done =)
Reference: