There is different ways to deal with that. Not all of them easier than backup the media to an internal drive
1) I think you can add the NAS as a source in xbmc and then use the xbmc file manager to copy files. (never used that myself)
2) You can mount the windows share from command line and copy it over
3) I have never needed 1) or 2) instead I have added desktop components to xbmcLive. This way I can do some stuff in a GUI when I prefer that from the command line.
Perhaps you should finish your backup either over the network via windows or with 1) and then learn some more about 3)?
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Live actually comes with a simple windows manager: fluxbox.
If you exit xbmc, login, and type startx you will start it up. Right click to get menus.
sudo apt-get install nedit arora rox-filer
This will give you the basic tools you need for browse the system and e.g. post the debug log on the forum.
This is a very basic setup and I normally wants some more functionality like sharing a folder with right click or accessing a share on the network. I also need a cd burner GUI etc.
In the previous version I used a stripped down gnome desktop but in 9.11 this screws up some stuff in xbmcLive.
A nice ligthweigt alternative is lxde with some components from xfce.
sudo apt-get install lxde xfburn arora
is a good start.
This is however a bit to lightweigt for me. Like I said I need a "full" file manager that handle network shares in the GUI.
Maybe there is something leight weight that is good enough but I dont know it. I have just added dolphin from kde3.
sudo apt-get install dolphin
Please note that this will drag in a basic kde3 desktop and overwrite lxde in startx. I am sure this is easy to fix but I dont know how. Simple fix is to install dolphin first and then lxde. It does not matter for me since I use NX server to run the desktop in the background while xbmc is playing on the TV.