So far as I can tell from the website, it's technically illegal for you to make a copy for someone else, though without listening to see if there's a license specified in the audio I can't be sure. I agree with sirana that, given the podcast nature of it, it would be odd if the author considered such copying to be a bad thing.
No mention of any copyright or license is mentioned in the audio. I guess silence implies consent.
You guess poorly. Silence implies standard copyright laws, which make copying for distribution technically illegal. Having said that, given the nature of the production and the fact that it's being distributed for free, I highly doubt that the author has any intention of enforcing copyright. Unless, of course, you sell copies of it, or use it a voiceover for a porn movie, or something. Copying to audio CD to give away should be safe enough, though it appears to be technically a breach of copyright.
If you want to go the extra mile to make sure you're not doing anything unethical / illegal, you could always email the author and ask him for permission to distribute. That way, there'd be no opportunity for misunderstanding.
But, if you want to be sure you're on the side of legality, you might consider buying the archive CDs he makes available.
The archive CDs are not an option; those are just more mp3s which I would still have to convert to CD audio. I'm considering it though, since it appears to be the only way to get shows #1 through #9 of Hardcore History. Currently I'm just going to make discs of shows #10 to the latest (hopefully DC will finish the third, final part of the Punic wars series before my stepfather's birthday in early December).
Well, they're an option, just a slightly more inconvenient one. If you buy a CD, convert it to CD Audio and pass on both copies (or destroy the original, or anything else to ensure they're not both used by different people at the same time*), then you can, again, be sure of being on the correct side of copyright law.
*As you already have a licensed copy of the MP3's, this is a somewhat pointless step, and could probably be safely ignored. My only point here is to spell out the steps necessary to be
absolutely sure you're not infringing on the author's copyright. If Mr Carlin had specified a license that his work was available under, it would be a lot simpler.