Accidentally read a wii softmod writeup months ago and would like to give it a try on my dormant wii. I'm not gonna show you how here as step by step guides were available on the net and I believe you can google it yourself. Be noted there are so many different guides for different version of firmware, don't do this unless you have a strong heart.
My f/w was upgraded from 3.4J to 4.2J, but the IOS and cIOS upgrade was a pain in the back. Black screen of some popular games launched from USB loader can be circumvented by the workaround found on the net too. My wii turned out to be a multimedia center after installing the WiiMC package. :)