Since moving back to the UK I've missed both programmes, though I have some highlights on CD. In theory you can listen over the Internet, but you need a decent connection, which until recently I didn't have. Yesterday I bothered to install RealPlayer for Linux, and listened to PHC, great! However, to my horror I discovered that CarTalk is Winblows Media Player, so I won't be able to listen to it!
If you live in the US please listen/watch your local NPR/PBS station, if you don't live in the US, then you have to view/listen online.