ASP.net ASPNET user and SQLserver Database

[Guest]

The VS.net 2002 and SQL Server client were at the same PC and the SQL Server
database was at another PC. The dataset and DataGrid were created
successfully. However, when trying to run a Web form with a SQL Server
table, an application error concerned with the null user name showed up.

Then I opened up my Northwind database, trying to create a login/user:
computername/ASPNET, for the database and Employee table. An error msg
popped up: Error 15401: Windows NT user or group 'ComputerName\ASPNET' not
found.

How do I solve this ASP.NET and SQLserver Security problem?

TIA,
Jeffrey