How where do I go in sound forge to record my line input?

How where do I go in sound forge to record my line input the on my soundcard that my mpc is hooked into?

Just hit the record button on the transport bar in SF or hit control+R and the record window will pop up so you can choose the device, mode, start time and so on.

Also, double click on the little speaker next to your time on the right bottom of your desktop, choose options, properties, playback or recording and you can choose from there. I also use Sound Forge 6.0