Inserting Posts from mysql db

I am trying to insert posts from a mysql database.

The script works ok apart from the fact that all posts go in the Uncategorized category. I have a field on the database which defines the category name ie full text version rather than id.

$cat=mysql_result($result,$i,”category”);
$post_category=$cat;

How do I get the posts to go in the correct category ?

Thanks
David