Fist off you should only see this if running SME 5.5
The old version of IMP (below 3 I think) used a different way to store addresses, they were stored in IMP its self.
Newer versions of IMP only run on the newer version of the Horde Framework, the addressbook is now a feture of Horde (as is IMP) so that anything that runs on Horde can use the addressbook (now called Turba).
I hope thate makes some sence...
Have a look at
www.horde.org for more info.