This tutorial will explain How to change the boot splash screen image for 10.04
Open the terminal and run the following commands
sudo cp /usr/share/applications/gnome-appearance-properties.desktop /usr/share/gdm/autostart/LoginWindow
Then logout, and you’ll see an Appearance window pop up. Change it to how you prefer it, then close it and login as usual.
When you have logged in after finishing the customizing, run this command to prevent the Appearance window from opening at the GDM screen every time.
sudo unlink /usr/share/gdm/autostart/LoginWindow/gnome-appearance-properties.desktop