i don't think you can upload non-itunes, non-cd songs to your ipod. just like you wouldn't be able to play songs from itunes on a samsung mp3 player. some proprietary crap. BUT i think if you burned a cd of the songs you're trying to upload, and then ripped them back into mp3s from the cd, it would just think they came off a cd. same thing if you want to transfer an itunes mp3 to more than 3 computers (ever seen where it asks you if you're sure you want to use one of your "shares"?)...something about the burning and reripping, that little byte of info is lost. an annoying process to be sure, but i think it would work.
Hmmm - that's odd. I had a ton of songs that I had downloaded a long time ago from Kaaza that I was able to upload on my iPod. I'm not sure why this would be a problem for you.
you can upload songs from kazaa, limewire, the old napster, etc. because they don't have a proprietary program written into the file. it's only for files that you've purchased from an itunes-rival site, like walmart or tower records or something, but i'm not sure if it effects ALL rival site files, or just some.