I have the custom 96x32 pixel banner made if someone would be willing to try importing the image into opening.bnr for me...
July 06, 2020, 07:58:54 pm - (Auto Merged - Double Posts are not allowed before 7 days.)
I finally remembered how.
For future reference: Download IrfanView 64, open your image with it and resize to 96x32 pixels and save the image as a TGA file. Download GCBanner v0.3 and use the command prompt to convert the TGA to a banner. Rename the new file to opening.BNR and drop it into the root folder of the Gamecube game.