If I plug it in when the pc is on, I can get it to work. The second I reboot, the secondary monitor is disabled and the only way to get it to turn back on is to unplug it and plug it back in.
I have had a 4870 card for 3 months running dual monitors without a problem. I just changed to a Dell 2408WFP and now the secondary monitor is not being detected. I opened a ticket with ATI to have them tell me I installed the monitor incorrectly. I will let you know if they ever respond back...
I just looked on the Dell site and it states that the response times for both monitors ( 2405 and 2005) is 12ms. If you look in the "highlights" section of the monitor description its right there.