I think that m4a files will play on the 505 (as it's specs say it supports aac files--which is what an m4a file really is (not sure why the different extension--probably just to make it more confusing!). This doesn't necessarily mean that the files would be able to remember where you leave off--as this functionality is built into the iPod/iTunes interface.
I love my iPod and find that it is great for listening to audio books--I use it much more for that than for listening to music. I highly recommend using a dedicated mp3 player (such as the iPod) that supports "resume" for listening to audio books.
Check out this thread:
https://www.mobileread.com/forums/showthread.php?t=24634
Dr. Drib--One thing regarding listening to audio books on your iPod, did you know that if you change the extension of the m4a file to .m4b before transferring it to your iPod, it will automatically treat it as an audio book (remembering file position and letting you change the playback speed on the newer iPods)? It will also add the book to the audio book menu on the iPod.
dordale
