1. I don't believe you can map a drive that way.
2. Direct DB sync will be too slow to be useful over any kind of dial up connection whether it's a RAS connection to your own network or linking to a file on the web since your local client needs to open and scan the entire file to update it.
Any shared file db will have the same issues. You end up using e-mail sync which means that A, B & C send their update packets to a coordinator in the office who applies all of them to the master DB, generates update packets for each of the remote users and mails them. The remote users dial in again to pick up their packets that they then have to apply to their own local DB's to sync them with the master.
The only options I know are are 1. Spend Kilbucks on a huge, true client-server CRM system and the server to run it on or 2. got the Web based ASP route (salesforce.com or someone similar.)
I've got a group right now looking at Salesforce to see if it may do what they need.
[sig]<p> Jeff<br><a href=mailto: masterracker@hotmail.com> masterracker@hotmail.com</a><br><a href= > </a><br>If everything seems to be going well: you don't have enough information.......[/sig]