Selecting from multiple tables

Hi,

I have two tables "Post" & "Reply" which (oddly enough) contain the posts and replies for a forum, like so...

Post
------
id
title
content

Reply
------
id
postid
reply

I'm now trying to create a search facility that will not only look up the posts and match the search term against the content field, but look up both Post.content and Reply.reply and retieve the results in order of relevance with Post.title as the title.

The problem is when looking up the reply table I need to cross reference the Reply.postid field with the Post.id field.

I've been fumbling around with such statements as...

"SELECT Jude_forum_posts.title
FROM Jude_forum_posts
WHERE Jude_forum_posts.id =
(SELECT Jude_forum_replies.postid FROM Jude_forum_replies WHERE MATCH (Jude_forum_replies.reply) AGAINST ('$searchTerm'))"

...but not getting anywhere. I'd be really grateful if anyone could let me know where I'm going wrong?

Cheers,

Daniel