The PC version does not have an invincibility cheat, but the PSX version does. However, the PC version has loads of codes that the PSX does not. My favorite is iamquigon, but if you're having trouble the perfection and happy code. On my walkthrough page, I'm actually working on the Mos Espa Arena level right now. With Jabba's Champion, if you're having trouble be sure to use your gun as much as you can while he walks out. He pauses in the doorway for a while and you can hit him a lot then. Also, don't be worried about backing away. Partway through the fight, jabba throws down a small health pack. Like most fights in the game, the jump and slash is generally the most effective way to fight. It does more damage and it hits you less.
[ August 13, 2001: Message edited by: Master Qui-Gon ]