You cannot have a Realtek SIS 900 PCI fast ethernet adapter with a SCSI interface. Why do you ask? Realtek and SIS are 2 totally different companies. And a PCI card is a PCI card... it cannot be SCSI and PCI both at the same time.
Questions we need answered before we can help.
Is your NIC adapter add-on PCI or is it integrated on the motherboard? If integrated on the motherboard, you will need to visit the mb manufacturer to get the correct driver or post with the motherboard info and we'll see if we can find it for you.
If it's a pci add-on card then you must determine who made it and visit their website for drivers. Or you can go to SIS's website and download a generic driver.
http://www.sis.com/products/sis900.htm
Realtek website =
www.realtek.com.tw/