Hi,
it's enabled by default. To access smartd information use the "smartcl" command.
for instance :# smartctl -a /dev/hdb | more
smartctl version 5.33 [i686-redhat-linux-gnu] Copyright (C) 2002-4 Bruce Allen
Home page is http://smartmontools.sourceforge.net/
=== START OF INFORMATION SECTION ===
Device Model: HTS548040M9AT00
Serial Number: MRL262L2G4TM0G
Firmware Version: MG2OA53A
User Capacity: 40,007,761,920 bytes
Device is: In smartctl database [for details use: -P show]
ATA Version is: 6
ATA Standard is: ATA/ATAPI-6 T13 1410D revision 3a
Local Time is: Mon Nov 6 21:18:28 2006 CET
SMART support is: Available - device has SMART capability.
SMART support is: Enabled
G.