Yep. ECS motherboards are generally poor overclockers. My ECS motherboard (a GF7100PVT-M3 which I suspect from the part number is a little more advanced than yours) has no overclock capability at all except for being able to select the FSB.
I was able to to get a 2.4 GHz E6600 to run at 3.0 GHz by selecting the 333 MHz FSB.
I'm not complaining. Mine was a freebie, part of a package deal from Frye's. Well, actually, it was about $200. And Frye's threw in a free Q6600.