Guidance on setting up PSTN on PC

I am new to this process and subject but this is what I am tiring to do.

I have a home office and use Skype as VIOP. I also have a PSTN landline that I am not using although it’s connected.

I want to run the PSTN line through the PC to allow me to have a choice of landline calls or PSTN.

I am running vista.

I just want a basic setup.

Any suggestions?