Additionally you can enter the sorting menu but pressing the ENTER button on your remote while viewing the Now Playing List. This will bring you to a screen to toggle - Folders (on/off) and List Sort (Alphabetically/Date).
As mentioned above "2" will toggle folders on/off, and "1" will sort Alphabetically or by date recorded.
Sony S2, SVR-3000, lifetime (11/02)-160GB drive upgraded 11/04 (limited to 137GB)
TiVo S2, 540 unit, lifetime (7/05)-250GB drive upgraded 5/06
TiVoHD, lifetime (10/09)-1TB drive upgraded 5/10