I want to connect a database that is located on centralized server. How can I use a windows form VB.NET application to access it? Is this possible?
How can I maintain a single user entry (e.x== used of INSERT command)?
Are both of the above things possible? If so, how can I go about implementing them?
Yes, you can use VB .NET to access a database. You'll want to look into things called "ADO .NET" or "LINQ to SQL" or "Entity Framework" for various ways of interacting with the database. There's no shortage of tutorials out there for getting started.
I'm afraid the second part of your question is unclear. Using a comparison operator instead of an INSERT command? Please elaborate.