Salesforce > Database webservice replication

We are looking for someone to create replication between our salesforce instance (via the salesforce API) and our backend Database (will involve developing a custom Web service) We want to replicate values into 4 tables in our database from 4 objects in Salesforce, however we will also need a update method we can call on demand to post a database record back into Salesforce as an update (in the event the data changes in the database, eg; customer updates address); Salesforce Objects are: Accounts *Logins *Cost Centres *Devices Custom webservice will need to be programmed in VB.NET, and communicates to a MS SQL database. Experience with Salesforce API would be ideal.