If your OS is Windows 98 and you decide to install the Realtek 8139C drivers, 

the procedures are listed as follows.

1. Enter Device Management in under Windows 98 Operating system.

2. Select the item of PCI Ethernet controller and remove it then reboot .

3. Follow the ˇ§add New Hardware Wizardˇ¨ to setup the Ethernet adapter, click the next button when the prompt is shown , 
   select the ˇ§Search for the best driver for your deviceˇ¨ and click next

4. Press the Browser button to search the path ˇ§D:\Realtek 8139C\win98ˇ¨  
5. Follow any prompts for Windows 98 installation disks and restart when prompted.