Retrieving A Value From A SQL Database In Code Behind

VWD 2005 Express.  I need to retrieve a value from a SQL database from the code behind a page and assign it to a variable.  In Microsoft Access I can do this using the DLookup function.  What I need to do is get the data that results from the following query into a variable:

SELECT [SystemUserId] FROM [SystemUser] WHERE ([Username] = @Username)

The name of the data source is SqlDataSource2

Also, in Access I can create a recordset from a query and then process through the recordset.  Can that be done in VB code in VWD 2005 Express?