directdraw problem in full-screen mode

Before I get started, here are my system specs:
AthlonXP 1700+
Geforce2 mx400 64mb
C-Media On-board sound
Soyo Dragon Plus m/b

I bought and made my comp about a year ago, yet I still have this problem. Whenever I play any game in full-screen mode that uses directdraw, my sound is very garbled, and above that, my computer is terribly slow. I can play games using the built-in software rendering device (like Unreal Tournament), but the problem is that i cannot adjust the gamma, so everything is very dark. Games such as Dark Reign2 and C&C Renegade only work in windowed mode. My video card and my sound device both use the same IRQ. I've tried over and over, through BIOS and by adjusting the PCI IRQ steering to manual, but I just cannot change the IRQs. I have DirectX 9.0, and DetonatorX for my Geforce (the newest driver package for my system direct from nVidia is missing some .dll file.) I've tried with both the drivers from the manufacturer's site and Microsoft for the sound device, but they don't help either. Would getting a SB Live help?