DVD video-audio sync

Approximately 4.5 minutes into a DVD disc the voice and video lose synchronization. Hardware involved is PC with Epox MVP3G motherboard, Samsung 6X DVD, SB-16 sound, and AMD K6-2 500mhz processor, 192 Meg SDRAM, and an ATI Expert 2000 32 meg video card with hardware DVD support. There are no other system conflicts or problems