Since you have a receiver and pc with a soundcard,
all you need is the software to copy psk.
You can make an interface but that is not needed
if you are just receiving. Just place the mic
near the speaker of the receiver, be sure to keep
the volume low so you don't overload the soundcard.
Here is no cost s/w for psk31http://www.digipan.net
Did you know you can also copy slow scan tv ?http://mmhamsoft.ham-radio.ch/
This software has a fee to register it for wefaxhttp://www.dxsoft.com/en/products/seatty/