network traffic causing computer to lag

I posted about this as an audio issue, got no responses. I'm going to try one more time.

whenever there's heavy internet traffic (upwards of 300 to 500 k/s and above), the system will lag, most notably if there is any audio playing in any application. the audio will continuously jerk and skip and there's no way around it.

this issue is new to my Windows 7 64-bit install (had Vista before). I already updated the network adapter drivers, video drivers, and sound drivers. I have an nforce 680i mobo, with 2.66GHz quad core, GeForce 250GTS 1GB, 4GB of RAM, and a Creative Audigy LE soundcard.

anyone recognize or know how to investigate this issue?

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