Query Based On 'does Not Exist' Condition

Let's say I have a table called 'forumtopics' that contains a field representing the topic's author. I then have another table called 'ignorelist' which has two fields; one represents another user and the other a reference to the aforementioned author. There can be many ignored authors for any one user.

For any given user, I'd like all the rows from the forumtopics table where there is no match for (user, author) held in the ignorelist table. Obviously it's easy to check for existence, but can the opposite be done in a single query?

I run MySQL 4.0.17.