I have installed both homebrew and bootmii and both work, but when I try to load my game files, it doesn't work. The game im trying to play is wwf no mercy. it is in z64 format under roms in my wii64 file. when I select it in bootmii, it says "failed to boot the selected file!" Please help!!!

Try to load game in wii menu.

You need to load Wii64 from the Homebrew Channel. BootMii is only for loading homebrew MINI executables.