ASP.NET and Sharepoint

Question

I have been asked to develop a ASP.NET application that will be the GUI to a document handling system. The system uses a Access GUI today with a SQL 2000 server as DB. As i see it i will develop it using C# in Visual Studio 2003. But then i am told that i should peek at Sharepoint Server and use that as basis for the application. Any thoughts about that folks?. I know little about sharepoint. All i have done with it is to test the service that can be installed on 2003 server. Is it so that if i am to use Sharepoint server i only have to develop web parts that will be implemented using some manager in Sharepoint? So i am asking you guys for advice here. Any thoughts are welcome, both ups and downs Best regards Trond