I can only speak to iPods. iPods don't use folders on the player. Instead, you can search for the songs through the song title, artist, album name, and genre. iTunes (the software used with the iPod on your computer) also organizes information this way, although iTunes does store the songs in folders on your hard drive.
When you put the songs on your computer (before you put them on the iPod), you can use iTunes to correct the tags before putting them on the player. iTunes will automatically generate at least part of the song's ID tag based on the file name. If some of the information is missing, iTunes will leave it blank, allowing you to fill it in later.
iTunes also allows you to set the version of the ID tag you want to use. My car's MP3 player will only understand version 1.0 and 1.1 tags.
I'm planning to buy a harddisc mp3 player (20GB) but there's one crucial feature: The possibility to navigate through folders on the mp3 player - even if the mp3 files don't have a (correct) ID3-Tag. I can't find a lot of information about that.
What players have this option?
Thanks a lot for any help in advance!