I have connected a DFRobot ethernet shield to a Duemilanove board and have tried uploading both the Web client and Web server examples. I have set the ip address to one appropriate for my network. The link and 100mb leds come on, but the web client app says "Connection failed". I cannot ping the shield from my PC with either app loaded.
Can anyone offer any advice or help?
Have you tried asking DFrobot for assistance?
Yes, I have, but so far the emails have just determined that I am connecting the shield via an ethernet switch, and that I am using the Arduino IDE example to try to test the board.
I had exactly the same problem and sadly no resolution. See http://www.arduino.cc/cgi-bin/yabb2/YaBB.pl?num=1266076206
I'm posting my problem in the thread, http://www.arduino.cc/cgi-bin/yabb2/YaBB.pl?num=1266076206/0#10 .
Seems we all have a DFRobot shield.
Hmm, not looking too good. I have sent mine back to the supplier for a replacement; I'll update once I've received it.
Mines all working. Turned out the ethernet switch had a fit. Swapped with a different one and it's working fine.
The eBay supplier received my ethernet shield back, tested it and it all worked fine for him. 
He has refunded me my money, so good service there, but I am no closer to getting Internet connectivity ...
Update: DFRobot card still not working. Ordered an official Arduino card from SKPang which works perfectly.
Perhaps this is shield / switch compatibility issue - ethernet switches should be universally compatible, but there might be issues - unlike hubs they traffic-snoop and might be more fussy.... Could try a cross-over cable direct to a PC to see if that works.
DFRobot card now working! I had to change my router (from a seven year old D-Link DSL-504) to a new Belkin in order to get DDNS. Now the DFRobot Ethernet shield works 