Unfortunately it is possible for TempDB to not be in simple recovery mode. Where I recently started as the DBA, they have an instance where someone in the past must have changed the mode to full recovery, then performed the upgrade to 2005. Since in 2005 and 2008 you can't change the recovery mode as someone mentioned, I'm stuck with it in full recovery mode and haven't found a way to change it. Fortunately, the log for this TempDB doesn't seem to grow out of control as was suggested.