Complex join statement

[eluser]crumpet[/eluser]
I'm programming a private message system for users. The table pmessages stores userID's in the field mRecipient and mAuthor. When I access a message I want to join both those fields to the field userID in the table users so i can display usernames instead of userID's

Is there syntax to do this in one query or do i need to do two...?

basically i want to join two seperate fields in one table to the same field in another table