Here are a couple of sites that I have seen, I can offer no comments on what headsets in helmets are like to use, never having had the chance to use them. You do see them frequently on racing craft so I guess that if you get a good one then it will be an aid to communication.
The sets at http://www.atlanticuk.free-online.co.uk/headsets.htm
appear to connect directly to the radio and make no mention of an intercom facility.
Whilst poking around I found http://www.rob-ice.demon.co.uk/
this is the site of a biker who has integrated an intercom, two way radio, fm stereo receiver and mobile phone setup into his helmets.
Hope that these two may be of some help its an area I would like to know more about too.