You’re talking about modifying the operating system of your Wii in a way that will break the EULA you have with Nintendo. This is a legal agreement between you and Nintendo, just so you know.
I have a modified Wii, and I must say I think it’s bloody brilliant. You can install the DVD-X mod and also emulator programs that will let you play SNES, Genesis, n64 and PS1 games. You can also install media players that can stream music to your Wii over a network. You can stream video too, but it’s not HD and isn’t great quality anyway.
On the other hand, Nintendo do not just go along with you doing this quietly, and ensure that their flagship titles – the games that everyone wants – are accompanied by a firmware update that prevents execution of homebrew applications. It generally takes the hackers a few weeks to find the exploits to update the homebrew channel to the new firmware.
If you buy a lot of games, this means that you will often need to restore your system to a virgin state, update your Wii, then go through the tutorials to get your homebrew apps back.
It can be something of a pain in the arse, but on the whole I think it’s worth doing.