SQL-Server CASE

Anyone have much experience with SQL Server T-SQL CASE statement?

I have some code that someone else wrote that looks like this:

SELECT m.messageID, m.isTop,
   CASE @Mode
      WHEN 10 THEN m.subject
      WHEN 12 THEN p.userID
   END
FROM Messages m
INNER JOIN People p ON m.userID=p.userID
WHERE [blah][blah][blah].

What I need to do is return something that is not the userID, but still have that name.  This did not work:

SELECT m.messageID, m.isTop,
   CASE @Mode
      WHEN 10 THEN m.subject
      WHEN 12 THEN pr.userName As userID
   END
FROM Messages m
INNER JOIN People p ON m.userID=p.userID
INNER JOIN Personalize pr ON m.userID=pr1.userID
WHERE [blah][blah][blah].

SQL dies on the "As"... (or, if I leave out the "As", it dies on "userID")

Any idea how I can do this?

Thanks,