You appear to be referring to autoresolution, not autocompletion.
Autocompletion is the process that presents addresses to you as you being to
enter an address in the To field.  Autoresolution is the process that will
suggest names to you when you enter comething into To and press CTRL-K (or
Check Names) or tab out of the field.  You can't change the former, since it
has nothing to do with the Contacts folder, but the latter can be controlled
by opening Address Book and clicking Tools>Options.

You may want to review the following article:
http://www.ingressor.com/autocompletetips.htm

Randy