I tried what Beej said, and in fact it works ; but with a big nono: once that you click on teh subscribe button, the episodes became grey out, so you need to download again all the files if you want to listen them!

The trick is to have the podcasts already subscribed, otherwise it will download again the files (the files downloaded get the same name but itunes add a 1 ad the end of the filename), but if you delete them the podcast will launch anyway, that is the proof that for some reason, it can read the file but can't realize that the file is already downloaded.

Is weird that some podcasts works, importing correctly even after clicking on the subscribe button, while others does not work at all :(

Apple: please do some smart things like importing podcasts in an improved way...80% of the people that has a mac has at least 2 computers and has 2 libraries (and many use teh fast line at work to download the podcast LOL)