I'm going to guess that your easiest out here would be to identify the wires/contacts, buy a corresponding socket for that type, then splice in to an old patch cord or mic cord of a type that fits your soundcard inputs, effectively creating your own patch cord.
The second option, would be to lop the end off the mic set, and connect a plug of the correct type for your soundcard. No patch cord needed, but you'd be modifying your micset, which you might want to avoid, and you'd still have to identify the wires in the cable, and determine which wire connects to which component on the headset. (a little cheap DMM would be all you'd need for this) Radioshack and the like sell all sorts of plugs so that fabricating your own isn't too terribly difficult, and if you don't mind ugly, just lop some cables in two, and use some crimps or wirenuts to make the connections.
Have a particular model picked out? If you can post a link to it, or link a picture. If it's a weird plug layout, the above suggestion may be useless.