Line-In Measuring

How would I measure the input coming from a line in port on a computer in blitz? I'm making a program that can measure voltages coming in through that port, but I can't find a code that will measure the input from the line in, and give me a variable in blitz.

Please help,
Thanks,
Crazidemon

Someone made a DLL for input/output to/from various ports a while ago... I don't know where it is though.