Creating a credential

Hi All,
I am attempting to do a "two hop" report using Reporting Services. I created a credential on the reporting server and created a user on the data server with the same name and password as the credential.
When I try to run the report I get an error that says logon failed.
Is there a step by step document on creating and implementing credentials?
I really would like to get this running.
Thanks to all,
RoyWhat is the type of data source? What types of credentials? Are you using SQL or Windows?|||The type is sqlClient; persit security info = true.
Type of credentials? I created a credential under security > credentials. This was done on the Reporting Services Server. I created a data source and from properties the radio button Credentials stored securely on the report server is selected. The login name and password is filled out. I have selected and unselected Use as Windows credentials when connecting to the data source but neither worked.
On the server with the data, I created a user "resolution" to match the credentials name.
I really need to get this working in order to prove to upper management that Reporting Services is the tool we need.
Thanks very much,
Roy
PS If there is an article about how to setyp credentials I sure would like to know about it.