Trying to better understand how SELECT rights are managed in a/my SQL Server db
You need to look at the Effective Permissions http://msdn.microsoft.com/en-us/library/ms178358.aspx

I've never understood why there isn't a version of fn_my_permissions http://msdn.microsoft.com/en-us/library/ms176097.aspx which simply takes a user.

To do that you have to EXECUTE AS the other user: http://sqlarea.blogspot.com/2008/04/fnmypermissions.html