IIRC, 3G Nanos are not supported by ipodlinux as yet. It's possible the developers are adding support right now, but until they get their site hosted again we'll have to wait to find out.
gtkpod/libgpod does support 3G Nanos though, so you should be able to at least add/remove music from the device with the original firmware. If you have access to a Mac or Windows box, it's advisable to put the ipod into disk mode (I think that's what it's called) first. I failed miserably after multiple attempts to get my sister's 3G Nano to work with gtkpod though, so that's all the advice I can offer really. It boggles the mind the way they force you to run iTunes just to tweak options (like Disk Mode) on the device itself - why isn't there a menu on the actual device for these options? A big part of why I hate ipods that is, but I digress.
My trouble helping my sister with her ipod aside, libgpod does support your ipod, and there are a few other apps that purport to support adding and removing music from ipods. Some of these include:
http://www.yamipod.com/main/modules/home/
http://www.floola.com/modules/wiwimod/
http://getsongbird.com/
(and obviously all the apps that support libgpod, like gtkpod, banshee, rhythmbox, amarok...)