Copying from client's DB to my office's Server DB

Hi folks

back at my company, we're developing an application in C# .Net that will be
ran by users as a normal stand-alond app on their PC (just like MSWord(r)
,etc...)
The app also allows the user to send their product's data to a SQLServer
database online, on our company's webserver,
so a portal or site could share the data as well.
What we are looking for is to do kind of a "mirror" of the Local Database
(in user's PC at his office)
to our WebServer's Database (at our office)
Each of our client will have a different database in our server

The problem is: is there any way to do this? The user we'll be using some DUN connection or at best ADSL. Any way to only update the last modified rows on Local Database?
Will BCP do the trick? how?

Greetings dudes!