Search with relavence using MATCH AGAINST

[Josh]

I've got a search running from PHP with the following SQL:

$results = mysql_query("SELECT DISTINCT ForumThread.id as threadId,
ForumThread.Subject as threadTopic,
ForumThread.ID as threadId,
ForumPost.Message as postMessage,
ForumCategory.ID as categoryId,
ForumCategory.Name as categoryName,
MATCH (ForumThread.Subject) AGAINST ('" . $search->searchText. "' IN
BOOLEAN MODE) as relevanceSubject,
MATCH (ForumPost.Message) AGAINST ('" . $search->searchText. "' IN
BOOLEAN MODE) as relevanceMessage
FROM (ForumCategory
RIGHT JOIN ForumThread ON ForumCategory.ID = ForumThread.CategoryID)
LEFT JOIN ForumPost ON ForumThread.ID = ForumPost.ThreadID
ORDER BY relevanceMessage DESC, relevanceSubject DESC
LIMIT 0, 10");

There are a few things I want to ask:
I want to get relevance by adding (2 * relevanceSubject +
relevanceMessage), this would produce a better sort