How do I get my Plantronic Gamecom 780 headphone mic to work on my Mac?

I own one of the older aluminum Mini Macs. Recently I purchased the Gamecom 780 headset and while I enjoy listening to music and can hear my friend just fine, I can get the mic to work. Ive tried it on a PC and it worked just fine, no problems. I did my research before I bought them and they should work just fine on Macs, even there tech support told me that it should work. Basically, when I try to use the mic, a ton of static blasts over whatever Im useing. Sometimes I can hear my voise in the static but its very hard to distiguise. Ive tried it on other computers, so I know its not the headset. Ive tested it in different applications and nothing changes. It has to be somthing with the computer. When I am in system prefferences, the input level is at its highest wether I decrease the input volume or mute the mic. Does anyone have an idea of how I might fix this. Thank you so much. Have a good one and I hope your never plagued with tech problems.