VoIP redirected to analog phone

Hi, Sorry if the question is redundant. I could not find it in documentation. Please let me know if the following scenario is possible.

2 users doing a voice chat from PC-PC. I want to install sw on one PC such that the terminal point at that PC is phone instead of speaker and mic. It essentially should behave like a normal (PSTN) phone from the user perspective, but the whole communication is via VoIP. I want to install this so that my parents don’t need to learn how to use computer (except start and shut down). It should be like, I will give a ring (from my gtalk or ekiga or any VoIP client on my PC) to the other end where the phone rings, they lift it and start talking. Please let me know if this is possible with Asterisk (and also the hardware I will need). Otherwise please suggest me if there are other software. Thanks a lot in advance.

Do you still need this?