Songbird used to work almost perfectly till version 1.2 but now it has stopped working (since 1.4.2) and they have also stopped maintaining the addon.. :X
i tried using gtkpod but donno for what reason, it didnt work for me.
The only software that worked is Floola. The better part is that it also copied the artwork and also lyrics which songbird didn't do. Though it sometimes fails to do so (the issue is with artwork and lyrics, the song is copied just fine)!! But, I am satisfied that atleast I can transfer songs to my iPod without booting windows through Virtual Box.
When I start the software, the iPod is detected but I get an error saying that "You dont have write access to the iPod". For that reason, I had to run it as root.
I tried using it on Ubuntu 9.10 64-bit with iPod nano second generation and it works just fine.
You can download the software from here..