Public Contact Folder? or Populate a GAL with contacts?
I had to do it for my company but put it in the GAL and also make groups for regions of members etc. Big pain in the butt.
Without getting into too much detail, basically have to write a script to pull data into LDIF strings, then run a DTS that puts the strings into a csv or Text file in LDIF. Then Import that into Active directory using LDIFDE. Again this takes a long time ;p, your best bet might be to find someway to create an LDAP directory to use but unfortanatley that wasnt an option for me because I had to create query based distribution lists for my company members regions etc.