OK, look in your owner's manual. That molex connector is probably the one. One pin is probably audio out, one is probably audio in, and one is probably ground. You can buy those connectors. I bought a mono cable from the store with the 1/4 phone jacks already connected. Then I cut it in 1/2 so I had two cables...one for audio in and one for audio out for the sound card. Then I soldered the other side to the Molex connector. If you get a ground hum, then cut the cables and put the 1-1 isolation transformer inline. They're cheap...you can get them at radio shack for about $2, I think. I'm not sure what's in the modem...probably is the same thing. You'd have to measure the voltage on each side of the transformer to make sure it's 1-1.
You could always just use the AF out jack to the sound card, too....
Moleculo
</p>