The connection you found going to the sound card is a game controller port, for a joystick.
With COM2 and COM3 in use, you might have a problem even if you do get the cam plugged in, because it will have to go on another COM port, and could conflict with either the mouse or modem, unless you have a different IRQ open to use it with.
You can get the cable that goes from the connector on the motherboard to the case at computer shops, just tell them what you need. I think some retail electronics stores might have them too, Radio Shack, CompUSA, etc.
Install it onto the motherboard and attach it to the case, then get into Windows Control Panel, open Add New Hardware and add a COM port. Then go to Device Manager, highlight Computer and click Properties, see if you have a free IRQ, go back to Device Manager and set the new COM port to the free IRQ and see if it works.
The other way to go would be to see if you have PS/2 mouse support for the motherboard, install the PS/2 mouse port (physical cable and plug) and that will free up the COM port the mouse is using and the IRQ as well, which could then be used for the cam. The motherboard manual should tell you if you have PS/2 availability.
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