First off this will involve installing a package that isn't default for FreeNAS, if this worries you then skip down a step or two to the link to download all the project files manually. All this involves is installing subversion for checking out the code and all necessary files for the project to run. SSH into your FreeNAS server and execute this command:

This will take a while to run so don't worry if it looks like it froze. You should reboot your server after this is finished for all the new settings to take effect. This is just so you can download the latest copy of the project.

Next step is to check out the project which can be done using the package you just installed. Choose a folder on your data partition for this to go because in an embedded install any other location would be overwritten on reboot. I made a directory in /mnt/Main/Content/.db/ (This is where I've chosen for all the databases for UPnP and DAAP to be stored along with the scripts for my server that I've written):

This will check out the latest copy of the code to a new folder FreeNASPodder in /mnt/Main/Content/.db/

If you're uncomfortable with installing new packages to your server and just want a copy of the project you can simply browse to http://svn.xp-dev.com/svn/bemasher-FreeNASPodder and download each individual file manually. The benefit of using subversion is that getting the latest version of the file requires only browsing to the folder it resides in and executing:

Once this is all done you've checked out a working copy of the code. There are a few minor things you'll need to change in the script and in the configuration file. First in bashpodder.sh you'll need to change podcast_dir to the directory that you'd like your podcasts to be downloaded to, do the same in select_podcasts.sh. Make sure this folder exists as the script won't create it for you, it will only create folders for individual podcast feeds inside this folder. Be sure to escape spaces with a backslash.

The next change you'll need to make is in feeds.list. This will have a list of the url to each podcast feed you'd like to download episodes from. Be sure to keep one blank line at the very end of the file it will skip the last feed if you don't.

If you don't want to download all the current episodes all at once run select_podcasts.sh from the shell using:

This will create the basic folder structure that all of your podcasts will go into and compile episode.txt files for each podcast feed in their respective folders wherever you specified podcast_dir to be. To download a particular episode just remove the url for the episode you'd like to download from the episode.txt of the cooresponding podcast. Then simply run:

If you'd like to execute this using cron in the web interface go to: System -> Advanced -> Cron. Click the add button and use the following command to check for and download new scripts however often you'd like:

Followup:
Good news! I've moved all of my subversion repositories over to GitHub, the latest code for FreeNASPodder can be found at http://github.com/bemasher/FreeNASPodder. And even better news: you no longer have to install svn or download each final manually, GitHub has the option to download an archive in tgz or zip format of the latest source files.