You may just want to spend the money on a dedicated sound card. USB will produce sound through emulation software which will tax your processor even more. Sound production takes a decent amount of processing. If you get a dedicated sound card you will reduce the strain on your processor and be able to use any headset on the market, not to mention a dramatic increase in sound quality. Your processor was most likely doing all the work for your on-board card too, so you may see a noticeable performance increase depending on which processor you have. I always look at these situations as, "If I need to spend more than 20-30 dollars to fix the problem anyways, I might as well spend a little extra money and fix the problem correctly."
Putting band-aids on it like USB emulation devices only decrease performance, can add to weird software glitches, and you'll end up giving them to a friend or throwing them out when you upgrade your system because you won't want to put a slow component in a system you just built.