Is there a Mac app that will download these torrent files and sync them to iTunes so I can listen to them on my iPod?
If you search for "automatic" in iTunes help, you'll find this:
Export files from other apps directly to your iTunes library
When you export the file from the other app, set the destination folder as Home/Music/iTunes/iTunes Media/Automatically Add to iTunes.
The approach is explained here: http://www.makeuseof.com/tag/automatically-import-downloaded-music-itunes-mac
Basically, you have your app (Transmission, in this example -- it's good) save the downloaded files into the "Automatically Add to iTunes" folder. iTunes will get the files from there and you should be good to go.