Use this guide
to softmod your bro's Wii. You will need a sd card, I recommend a 1-2gb sandisk sd(non sdhc) card.
Unfortunately there is not a way to do it without a sd card. and I recommend that sandisk card because some cards will not work with the hackmii installer.
That guide will get you the latest and up to date softmod possible.
NOTE - And be careful, Wii softmodding is very addictive.