It's a common issue with those. Read http://www.driverheaven.net/archive/index.php/t-8781.html
Right after de-fragging my computer today, I noticed gaps in sound in video games and music files. I ran the DirectX Diagnostic Tool, and when it tested the sounds, it came up with this error:
"mono, 8-bit 22 Khz, from a software buffer"
"DirectSound test results: failure at step 19 (user verification of software) HRESULT 0x00000000 (error code)"
My computer has a C-Media Rear Panel Audio soundcard and a Logitech USB headset. I updated my drivers as best I could--do I need to reinstall Windows XP?