Can not having a sound card lag up your game???

do you mean having a soundcard that isn't the motherboard onborad sound? if you do then not likely, motherboard sound uses around 3% of your processors usage, so having a separate card mibbee wouldn't make a (notable) difference.
Although getting an creative x-fi wouldn't be a waste of cash just because they are the bees knees. And according to creative they have something like 24 x more sound proccessing kick than pentium IV

Motherboard sound usualy tops out at 44khz, thus using a small percentage of the cpu, and the more cpu usuage > the less the frame rate > more the lag. The cheaper the soundcard, the less likely it will have it's own processing unit, therefore a clear 96khz will use more of the cpu resulting in small frame loss overall and more at heavy times. The X-FI's on-board cpu, while being a chunk of change, will allow you to have beautifuly clear sounds without using your AMD 4000 crunching to process them, freeing it up to process the frames. I'd likely bet the X-FI would be the last soundcard you'd have to buy, @ 32bits and almost 200khz, the soundcard side of the industry is topping out. If you happen to buy an X-FI, get the whole 'shibang', remote, 3 1/2 inch tuner drive, ect. Make it worth you while. We may hit 64bits, but you'd have to have a crazy amount of 'voices' going on at one time. I can't remember if 32bit can process 32 voices or higher, but think about that in a game :? Woa!

Topped out! 8O

Kudos.

You are ignoring all the positional 3D code, the effects that go into each voice (such as distance, reverb, materials, EAX 2.0 - 5.0 HD, and the game code loop + DirectX offloading required to process audio).

Audio uses more than 10% of peoples CPU power at times, and when there is heaps going on a 'soft sound card' (eg: a chip that then re-offloads back to the CPU) really hurts performance. (Heck, the game code pushes it via DirectX using Audio Engine, then DX pushes to the Audio chip [hardware acceleration], which pushes it back to the CPU [what I call hardware deceleration]).

Considering how much CPU power this can use, (not 'on average', but 'during re-creatable worst case scenarios, eg: heavy action in an online FPS') gamers really need an Audigy 2 at the least, if not an X-Fi XtremeMusic (but nothing more costly, as they all provide equal audio processing performance).