Any chance of sharing how you did it 
Sure. It's not that difficult.
Changing the startup screen is in the manual. I uploaded the splashw.bmp image file (see below) into the gps root directory using Explorer (My computer recognises the GPS as a storage device when i connect it to the computer). You can also copy images to the 'photos' folder on the GPS and use one of those as the startup image through the GPS preferences menu (preferences > start up preferences).
splashw.bmp (converted to a .jpg):
Through explorer, i browsed through the GPS folders and found that all the car icons are in the '\art\cars' directory. I copied one of the car icons onto my computer, modified it in photoshop, then copied the modified image back onto the GPS.
The red around the car is necessary. The GPS will make the 'red' transparent when the image appears on the GPS screen.
Both images 'were' .bmp files, but photobucket converted them to .jpg files when i uploaded them for 'net viewing. If people are interested, i can try to upload the actual .bmp files for people to use as they wish.
NOTE: The .bmp files are MUCH cleaner than the disgusting converted .jps that photobucket butchered.
Anyway, that's how it's done on the tomtom go 730, i don't know if it will work on other units.
Good Luck!
Tim.
