You get your Gamecube modded. You burn the ISO or mount the image to a DVD or CD. You press power and enjoy.
Here are two links to gamecube chips:
http://www.xenogc.com/
http://viper-chip.com/features.html#vgcx
Here is what the first link says:
:: Chip Features
+ compatible with all regions & all versions
+
direct boot of DVD+-RW media
+ supports multi-disc games
+ supports Action Reply
+ region free loading
+ super easy wireless install
+ no need to remove mainboard
+ PAL/NTSC region force
+ installation control LEDs
+ switchable read setting adjustment / error retry
+ switchable audiofix
+ anti-static packaging
+ very low price
+ selfbooting homebrew linux discs (thanks to Isobel)