You won't be able to just drop the Itunes songs onto another MP3 player. MP3 uses MP3 format and Ipod uses AAC I believe. There are free converters to convert songs to MP3 format. I have Itunes for the Ipods and copy and save the songs to the desktop computer in a folder. Then I convert them into MP3 for the SD card in the vehicles. Works great, just a few extra steps.
iTunes can convert to MP3 for you but if it's already MP3s you put into itunes it leaves them that way and If you are putting your CDs into it you can tell it what format you want it converted to.
I think it only converts the files to AAC when it puts them on an ipod. I think it tells you AAC has better sound quality but I always set it to mp3 anyway because of that compatibility problem. 
