I've looked into this a bit when I got the Homebrew Channel, and from what I found, getting the system to play PAL games is extremely complicated. Then again, I think anything that is more than simply selecting an application to run from the Homebrew Channel is complicated. Anyways, it looks like the hacks I've found will not play from discs, and instead, the game must be run from a hard drive (which in itself can be a mess to get working). So this means you either have to download the game from the Internet, which is illegal, or find a way to copy Wii discs, the legality of which is questionable. After that, not every game will function, and absolutely no games will work 100% correctly due to the differences in PAL and NTSC televisions. If you're going to hack your system, it is strongly recommended that you create a backup of your internal memory data. Should you happen to brick the system from a hack, you can restore it using the backup.
In short: I'd give up that dream of playing PAL games, as I have.