Yeah, when I first got BF42, I would lag badly. I lowered all the graphics and everything and I couldn't figure out why I was still lagging. I saw the sound settings and said "what the hell, I'll give it a shot" and I lowered them. BAM! It was like magic, my lag was gone entirely. I couldn't believe it, I could crank up my video settings to full (not much of an accomplishment now but I got BF42 when it came out and my comp was already a couple years old and hadn't been upgraded at all) and be fine but the sound was lagging me.
I have a Realtek HD Audio Output, is that a good enough soundcard?