This a bootsplash verbose and silent theme using the fbsplash program. You can find full documentation on howto install the theme and/or the fbsplash here:
http://fbsplash.berlios.de/wiki/doku.php

On Gentoo to install:
1. emerge -av splashutils (with the fbcondecor USE flag active)
2. rc-update add fbcondecor default
3. Goto /etc/splash
4. Uncopmress the Underworld archive in that folder.
5. Assuming that you use the latest gentoo kernel, issue this command:
splash_geninitramfs --verbose --res 1024x768 --append /boot/initramfs-genkernel-x86_64-2.6.30-gentoo-r4 Underworld
If not, just check the name of your active initramfs (in grub.conf) and replace it in the upper command.
6. Append this to the end of your /boot/grub/grub.conf file on the line describing the kernel parameters:
splash=silent,fadein,theme:Underworld console=tty1
7. Run grub-install with the needed parameters. For example if your boot manager grub is installed in the MBR of your /dev/sda then:
grub-install --no-floppy /dev/sda
8. Reboot


You also may like the KDM4 Underworld theme: Underworld KDM4 Theme
http://www.kde-look.org/content/show.php/Underworld+KDM4+Theme?content=110202

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Image taken from http://www.skins.be (http://wallpaper.skins.be/kate-beckinsale/22486/1024x768)