Try using the IBM DB2 for I IBMDA400 OLEDB Provider included with IBM I Access.
I tested it briefly with Excel 2010 and it worked perfectly. The driver can be installed directly from the IBM i system using the UNC path \\system\QIBM\ProdData\Access\Windows\cwblaunch.exe.
How to configure the Microsoft OLE DB Provider for DB2 to connect to an IBM I (AS/400)
The optional Data source parameter names the Universal Data Link (UDL) file in the settings are saved.
The Network parameter must be TCP/IP Connection. You must click the ellipsis and configure the IP address of the IBM.
The Security parameters are self-explanatory.
The Initial Catalog parameter refers to the relational database name configured on the AS/400 system. It can be found with the DSPRDBDIRE command from a terminal session. The default is the system name (serial number) or RCHASE12.
The Package Collection is the name of a library where temporary objects required by the Microsoft OLE DB Provider for DB2 will be created.
The Default schema is the name of the default library for unqualified objects.