See links to Apple.com
Plug in your iPod and don't press "Sync".
you can burn the songs you want to sync onto a CD and then download them to your iPod from the harddrive
You can use Napster for songs, and other legal places to get songs and videos.
This ipod manage software can transfer the files from ipod to computer, ipod to iTunes, and iPod to iPod: http://www.ipodtransfer.net/how-to-transfer-ipod-file-with-ipod-transfer-software.html
get iexplorer
first thing is when you connect your ipod highlight your ipod and select music and check manually manage songs and there you go you can sync songs without syncing to that itunes library.
you have to put in your code
well if it's on your ipod set your ipod to manual manage music then drag and drop your music without erasing your music
Not without erasing the jailbreak.
It is not allowed.
Depends on the size of the iPod, the size of the videos you want to put on and the total size of the 425 songs on the iPod