Hi all – looking to do the above using preferrably free, virus free software.

Any ideas please?

Do you mean AAC files? If so, those are Apple’s native music files, in which case the really obvious choice of free ‘ware would of course be iTunes, which is quite happy to allow you to select tracks and convert to MP3, in whatever bitrate you want. Don’t know quite why you’d want to other than using a devise other than an iPod. AAC files at high bitrates are better quality than MP3’s.

No, I mean aa files, but cheers for trying 🙂

It’s the format favoured by Audible (audio books – sad I know!!).

http://www.topvideopro.com/audio-ripper/aa-to-mp3-converter.htm

Dunno if it works but i guess it’s what you want!

Just to update, and for anyone interested in listening to audio books, don't bu99er about with software – buy a Sansa Clip.