Audio/Video Stutter (Windows Media Player, QT, RP)

Whenever I play an audio OR video file in Windows Media Player, Quicktime, or Real Player, the audio and/or video stutters for about the first 30 seconds, then plays normally. It only happens when loading a new file. If I'm playing a playlist, the first file does it, then all the rest play flawlessly. It doesn't matter the audio/video type, size, or length.

This problem is also present when playing audio/video in my web browser (Firefox, IE, and MSN all the same), but if I close my brower window or tab without stopping the audio/video first, my browser freezes for anywhere from 5 seconds to 3 minutes before it closes. This is driving me insane! My PC has never given me problems before. I've updated all video and sound drivers and chipsets, and have the latest versions of the media players, codecs and DirectX. All I can think of to do right now is defrag. Any other help would be greatly appreciated!

-Big Sonny-
CPU: Intel Pentium 4, 2800 MHz (21 x 133)
MB: MSI MS-6701 (Medion OEM)
Video: nVIDIA GeForce FX 5700LE 256mb
OS: Windows XP Home SP2
Sound: Realtek AC97 Integrated
HD: Seagate Barracuda ATA V 120023 120GB
Ram: Samsung M3 68L6423DTL-CB0 768mb PC2100 DDR