For the ipod just let itunes to add your music to the itunes library and it does it automatically. You don't need to do anything. With other players I know that if your use WMP all you have to do is add the files the windows library, once again you don't have to do anything. As long as your music is in mp3 format you do not have to convert. Every player (save for most sony players) except mp3. So as long as you don't buy a Sony player you are safe. You need no 3rd party software or anything. For HD players check out iPod 5G, Creative Vision M, Cowon iAudio X5L. Those are the newier genertaion models that also play video. They are all great choices.
I am looking at MP3 players at the moment, and althought he iPod is impressive am wondering if there are any players that I would have an easier time converting my music to. Right now I have all my stuff organized in folders by Album, and I really don't want to have to reorganize it and find my album info (esp. pics again). I'm wondering if there are any HD based players that either use this format, or would let me automatically convert from it (for that matter, does iTunes automate this?)? If not, is there third party software for iPod or another player that would convert my folders to the database format for the player?