Lot of dependencies on that question.
It would only have a chance to make a difference if your computers performance is CPU limited, not graphic card limited. A situation where the video card is waiting on the CPU.
Even a cheap sound card has advantages over a onboard sound chip, IF the cheap sound card has onboard hardware buffers exposed to DirectSound (the sound component to DirectX). With onboard hardware buffers, the sound chip is free to run in parallel with the CPU, as opposed to stopping the CPU each time it needs to fetch data from system RAM.
