So, Microsofts Sync Framework will help with this. Introduction
Couple of issues stand right out at the beginning.
If you are going to have the data exisit on the client first, then sync to a server at some point later, you need to think about what happens when a number of clients all sync to the server, esp. around conflict resolution.
There are events that get raised on the server side to idetify when a conflict occurs, but you need to decide who wins. (one on server, one from incoming client). Depending on wht you choose to do here, the second sync is likely to modify the client data.
Think carefully about what to sync. If its a contacvts database, is it good enough to have just the client name and telephone number sync, or do you need to whole contact history as well?
Think in terms of syncing a table, using rows where the key is all the same value. Even if this is a constructed table with triggers etc. This makes the framework sync a much simpler process and less prone to errors (tables needed to be synched in different orders).
If its an invoicing program, maybe an upload only table of orders is needed, with all the assoiciated invoice, history, reporting tables etc being updated on the server, rather than updating them on the client and syncing multiple tables....