XP Sound problems

I have problems with XP and sound. What happend is when i’m in games particurly the video clips the sound cuts in and out. I have tried everything i can think of and still it has this problem!! I have an AMD 1800+ CPU with a gigabyte 7DX+ motherboard, geforce 4 video card. I have disabled the onboard video and put in a Vibra 128 pci sound card but it does the same thing!! I’ve got all the updated drivers, flashed the bios.
Any idea’s would be appreciated before i see how well this computercan fly!!