Logon Credentials

In .Net, you can program logon credentials like this, for example:
(PRF is a web service)

PRF.Web_GetDataService x = new Web_GetDataService();

System.Net.ICredentials y = new System.Net.NetworkCredential("sfci", "shopint");

x.Credentials = y;

This code does not work in VBA. I am trying to do the same effect in Excel 2003 VBA. Does anyone know how to translate to above logon credentials code into Visual Basic?