Converting ATRAC (Sony Sonic Stage) files to MP3 and importing to iTunes

Does anyone have any experience of doing this successfuly and guidance on how to do it? Additionally, this would make my iTunes library much bigger than my iPod nano can store, so I'd need to get a bigger iPod. Would I encounter any difficulties, in terms of copyright protection or limits on amount of transfers, in transfering tracks to the new device (whether from exisiting iTunes library or tracks converted & imported from Sonic Stage)?