Why do Repeated Records in a dataset appear?

I first develop a multi_layer MIS ,using SQL Server DataBase and Delphi
tools .
Now after completing it ,I want to develp the demo sample about this , i use
Access instead of SQL Server 2000,there appears many problems ,one of which
is that in every datasets of the client ,there are repeated records .Why
does this exist?How can I deal with it?How can I correctly develop a demo
sample for my origin products?
Thanks in advace.