To make custom screens on the G15, you need to have the program
LcdStudio. This program allows you to make your own designs for any external lcd screen you own (including the G15 lcd).
To make it look like mine, however, it must access information from many different programs, in order to display real-time data. For instance, on my design, it takes the GPU temp data from
RivaTuner, the CPU temp data from
SpeedFan, and the FPS data from
FRAPS. From there you can display the data on the screen however you'd like and add text and graphs. It wasn't shown on the picture, but my design implements a FPS line graph display under the number showing recent FPS history, so you can determine if the lag spike you had was your FPS or internet connection.
I can send you my design if you'd like, but as I said, you will need all the programs mentioned above installed, correctly configured to give out data, and always running in the background.