05-30-2011 09:48 AM
Here is the link to the service manual for your computer. The procedure for adding PCIx1 cards can be found on page 54.
If you cannot find a PCIe x1 network adapter, I recommend you install an external USB network adapter.
The PCIe x16 slot is only for a video card. Several people have unsuccessfully attempted to install a PCIe x16 network adapter and the PC will not start up.