How to change loading screen :
1.) Find a picture that you like. Download and save it as a bitmap (bmp) file

2.) Resize the picture to 800x480 (for iGO8.3)

3.) Make a copy of your picture and name it loading.bmp

4.) Copy branding.zip from your Igo8 SD card to your computer (Keep a backup copy)

5.) Using WinRAR, open branding.zip (by double clicking on it) and find \ui_igo8\800x480 and add loading.bmp to the archive (by choosing the ADD button in the top left corner of Winrar and then navigating to where you have your loading screen picture saved on your PC) overwriting the original "loading.bmp"

6.) Copy branding.zip back to yor SD card overwriting the original (make sure to keep copies just in case)

8.) Abracadabra when you start iGo8 you get a fresh new loading screen

thanks to Darkoz

AND HERE IS MY VARIATION BY coopv2.......... DO A BACKUP TO YOUR HARD DRIVE FIRST.

But found it easier to do this.... inserted my GPS card into my USB reader, and open the iGO file to reveal the 'Branding.zip' and 'data.zip' RAR files. BUT DO NOT EXTRACT.
JUST right click on data.zip and select...open with.... Compressed (zipped) folders. this will allow access without 'extracting' the contents.
you can then go to the ...\ui_igo8_da Folder and select 800x480 folder, and find the image marked...."loading.bmp" then select your new image from your modified graphic, that you also named..."loading.bmp" cut and paste to ..800x480 . you will be asked to replace existing file, select yes.
THEN do the same in the 'Branding.zip' RAR. .AGAIN , DO NOT EXTRACT RAR.
When you back out of each zip it will save.
I am no expert and only learned this the other day.

EDIT: Different resolution may require some thought on your part.