I just picked up a 360 2 days ago. It was the premium system and comes with a headset. The heaset jack looks to be the same as my original xbox headset. On the 360, there is a mini jack on the bottom of the wireless controller that the headset plugs into, and it looks just like the one from the original Xbox. So I think it should work, it's the same kind of port.
By the way, CompUSA is selling the premium 360 for $399 plus you get another wireless controller for free ($50.00 value). No rebates or forms to fill out, they just give you the controller right there. That's where I picked up my 360.
Good luck, you'll love it.