Since I dont use the equipment you have, I dont know if your headset is a separate "sound card" in itself, or if it depends on the one recognized by Windows to function. I'm assuming from the issues you had before with this setup that it is a standalone sound device.
Your "problem" is, in all probability, a combination of problems. First, if this is a standalone sound device it shoud be listed in the hardware manager once you have drivers loaded. If its not, and it doesnt recognize your device, or doesnt recognize it during driver installation, there might be a problem with your USB port. Do you have any other USB devices? If so, are they working properly? If they are, try unplugging them and plug your headphones into that jack, see if you can install the drivers now. Plugging the headphones into the output jacks from the computer wont do a darn thing if your onboard sound chip isnt functional.
As for that, Crystal Sound Fusion manufactures millions of onboard sound chips for installation on motherboards of every type imaginable. And they all have one thing in common. They all sux. They are as common as dirt, and work about as well. They are notoriously buggy and incompatible with a double-handful of games I can mention, and probably more I dont know about. Add to that the fact that you have an older model chip, running under Windows 98. Dx 9.0 wont be compatible with any of your drivers, as Microsoft stopped supporting Win98 a year ago (this is not a knock on Win98, I still like it better than XP, but as time goes on it is going to be harder and harder to find drivers for stuff). Taking all of these into account, you probably wont find a truly updated driver for your model of Crystal soundchip. The originals should be on the restore CD you got from Gateway with the computer. You can probably get an update for those, but it still wont be any later (more than likely) than mid-03.
My reccommendation to you is to go into your BIOS setup and disable the onboard sound. Yours might be a jumper on the motherboard even. Then you can concentrate on getting your headset to work without worrying about the onboard sound interfering (this is still assuming your headphones operate independantly of need for a sound card). Then if you decide you want exterior speakers later, you can buy a soundcard and add it on.