VB .Net Application

Question

I have a Application In Vb.Net .I am Developing This Application on Microsoft Visual Studio 2008 , VB.NET, Sql Server 2005 , Crystal Report.

And That Application Have Registration Form . Now My Question Is This Application is Installed On 5 different Computer In a Network . At the Mean time all 5 users
are Open Registration form Then They click on Save button on same time . I Have a table registration , and that has a column (code) that is primary key. whenever they want to save the record only one user can get save the record . all 4 users are rollback the transaction because of primary key violation error. Therefor i want to generate code on a queue basis .. where user can wait to get a Unique Code of that Record and i don't want to users request to rollback ...