10 to 100mbps upgrade. CAT-3 to CAT-5

On 568B configuration,what is the function of the blue and brown pair? Do I even need it? I work in a place that we have cable folks that is incharge of the wiring. And this guys are only using the orange and green pair out of a CAT-5 cable, they cut the blue and brown pair. Is this correct? Will 100mbps run on 2 pairs and be stable? I will need a hard copy to show this folks if what they are doing is wrong.

Thanks,