How can I sync the address books of multiple computers running Outlook, without using Exchange?

I am looking for a cheap enough solution to implement at a customer’s network. They need eight computers to be synchronized in terms of contacts.

The one program that appeared to be closer to what I need is GO Contact Sync (http://www.webgear.co.nz/Products/GOContactSync.aspx) — it worked with 8 contacts but then it seemed to fail with 1300+ contacts… it hanged and didn’t recover overnight.

I am going to try again with this software but I’m just not sure…

So I’d like to ask you for recommendations for this purpose, that are the most inexpensive, and that don’t need Exchange.

Thanks for all the input!

Best,

Rex.