I would try setting Quicktime's playback device to "wavout" first, as it is the simplest step to try:http://www.worldstart.com/tips/tips.php/3174
If the problem persists, try iTunes troubleshooting steps for video jumping problems. Although the help files are for video and not audio, there are sections that might help improve your audio issue. I couldnt find anything specific in their website to troubleshoot audio only.For XP/2000
- read the part "Modify your System Drive Configuration" (near the bottom).For Vista
- read the parts "Modify your System Drive Configuration" and "Disable ReadyBoost on Flash-Based Drives" (near the bottom).
Post back with the results (along with your OS and amount of RAM if these steps did not work) - and good luck