Maybe you could create a file path to one address book that is shared on network.
Files can be shared between PC's and accessed on a local network if done right.
This is based on outlook 03...don't have 07
Take a Personal address book file and put as shared on network. Then set this PAB on each computer aiming toward this file. so anytime a new email contact is added you are all adding to same file.
This is all theory..I have never attempted it. So attempt if you wish.
To set PAB go to outlook tools, then email accounts, add new address book,additional address book,personal address book..then aim path at the shared file. do this for all PC's.