There are a few things to consider...
The main question is whether or not you will be live streaming, or simply recording--the answer will determine which path you will go down.
The podcast recording scenario is the simplest when considering how to capture the Skype feed. There is a Skype add-on app called Pamela Call Recorder that can capture and record your Skype call. I am sure there are other options out there, but this is the one I have used with ease and success.
Live streaming is a completely different scenario. The objective is to capture your mic audio AND the Skype audio together, which means mixing 2 different signals together. I have experimented with many different configurations/options and the one that seems the most straight-forward and makes the most sense to me is this:
- Use a non-usb microphone into an external audio console for your mic audio
2a. Route the Skype call through the internal sound card of your PC/Mac, taking the audio out (via the headphone jack) and feed it into the audio console
2b. Following the instructions in 2a, but making the Skype call using a 2nd computer, thus freeing up the internal sound card of your primary machine...
3a. Using a second (external) audio interface, feed the main mix out of the audio console into that interface. This will be your main feed for your stream.
3b. If using a 2nd computer for your Skype call, you can use the internal sound card on your primary machine for the stream's main feed...
Now, to get your audio for the actual podcast feed, there are a couple of options:
- Record your feed directly from your audio console
This option requires another available sound card. From the audio console, take an auxiliary feed--either an aux send, if you have one, a 2-track/tape-out feed, or (kind of a stretch...) split the left/rights off of the main feed to the stream, and run them into the available sound card, which is then routed to your DAW/recording software (Audacity, etc...)
- Use a recording from the live streaming service
In my experience, live streaming services like Ustream or Mixlr either have an option to, or does by default, record your session. In the case of Ustream, I have recorded sessions, and then downloaded the file (.flv format, I believe...) and run them through a utility that saves the audio from the file as an .mp3 file, which I used for the podcast.
Option #2 is the least complicated and least expensive of the 2.
I'm sure there are many other creative ways to accomplish this, but this is the conclusion I have reached after a lot of pain and searching for a solution to both record the podcast AND live stream the session.