How to Create a Theme in CentOS 4.3

The themes are located in /usr/share/gdm/themes/<some-theme-name>

For instance the GdmGreeterTheme.desktop

[GdmGreaterTheme]
Encoding=UTF-8
Greeter=circles.xml
Name=Circles
Description=Theme with blue circles
Author=James Smith
Copyright=(c) 2002 James Smith
Screenshot=screenshot.png

To test the theme you built, you need to install/yum the Xnest package.  Once installed, type:
gdmthemetester xdmcp "theme-name"

If you like what you saw, to set it for good, edit the gdm file in /etc/x11/gdm/gdm.conf:
GraphicalTheme="your-theme-name"

In the xml file, you can modify the row of buttons.
Position if changed from -0 to 0 moves from right to left
Anchor will put it on certain area on the screen.  Possible choices are: N, S, E, W, NE, NW, SE, SW

To remove the log on loading box when you first login, edit the file located in /usr/share/pixmaps/splash/gnome-splash.png

To modify the screen resolution, the settings can be found in the /etc/x11/xorg.conf file.