no DataSet option with intellisense

Hi,

I cannot get the DataSet to work with .Net Framework 3.5. I had no problems in 2.0 but for some reason, the DataSet option does not show in the intellisense. When I manually type in DataSet ds = new Dataset() I get the following error. Maybe I'm just overlooking something?
Error 1 and 2. The type or namespace name 'DataSet' could not be found (are you missing a using directive or an assembly reference?) 

//Create a select statement to gather employee info from MISA
string selectSQL = "SELECT dbo.Employee_data.First_name, dbo.Employee_data.Last_name, dbo.Department.Description, dbo.Employee_data.Employee_id,dbo.Employee_data.Log ...