OK, I said I was out, but this is new ground. It didn't look to me like PPCTechs said there was a CF audio in card coming, it looked to me like they were going to make an adapter. They already make one for 2.5mm headset jacks. What is needed for those PPCs that have audio in, some Toshibas, the Dell x50, maybe others, is a 3.5mm version of that adapter. You can already get various ones from
http://www.pc-mobile.net/toshiba.htm. I bought too of the ones for the Toshiba from pc-mobile and they work fine on my X50. The one that has a single earbud and cord mounted mic makes a great Skype accesory.
As for Audio in via CF card, that exists too.
http://www.core-sound.com/HighResRecorderNews.html for $199. Why so high? because the CF card doesn't have audio capability. What they had to do is cram a digitizer (encoder) into the CF card, create the digital file and then just transfer the file over the CF interface. With the development cost and limited market, the price is high.