Does anyone know how to connect an Ethernet Interface Board to Arduino? http://www.sparkfun.com/commerce/product_info.php?
Your link to Sparkfun is broken, please repost the correct link and we might be able to give you an answer. :-)
I'm not familiar with that board but given that it mentions an 8-bit data bus but not SPI, I suspect supporting it is likely to be non-trivial(TM).
My suggestion would be to consider one of the more commonly used Arduino ethernet solutions.