How to change Ubuntu 10.04 login screen image

Execute the following command in a terminal,

sudo cp /usr/share/applications/gnome-appearance-properties.desktop /usr/share/gdm/autostart/LoginWindow

Copy an image to /usr/share/backgrounds

cp yourimage.jpg /usr/share/backgrounds

Logout Ubuntu.
You can see a window will pop up, select "Wallpaper" and locate the desired image. You can change the image from there.

Login to system and open a terminal and execute following command,

sudo unlink /usr/share/gdm/autostart/LoginWindow/gnome-appearance-properties.desktop

Switch from Unity to Gnome in Ubuntu 11.10

Enter the following command in Terminal,

sudo /usr/lib/lightdm/lightdm-set-defaults -s gnome-shell
Reboot PC. 

Format and rename USB drive using commands

Plugin your USB Drive.

And execute the following commands via Terminal.

sudo umount /dev/sdb1
sudo mkdosfs -n 'YOURNAME' -I /dev/sdb1

How to change boot theme by using Plymouth Manager

Plymouth Manager Installation
Open a terminal and apply following commands,

sudo apt-add-repository ppa:mefrio-g/plymouthmanager
sudo apt-get update
sudo apt-get install plymouth-manager

Plymouth Manager will appear in Applications > System Tools