I've been wondering if there was a version of MAME (Multiple Arcade Machine Emulator) available for Wii, and finally managed to find one that works. Had to spend a bit of time faffing around to make it run for me, but it's well worth a look.
Download MameWii, and the way I've set up my file is to:
Take the mame folder out of the mame-wii-v1.0 folder and put it on root of your SD card
Take the sdlmamewii folder out of the mame-wii-v1.0 folder and put it in the apps folder of your SD card
Put your roms in the rom mame/rom folder (I included as many version of the roms as I could, to try to get better compatability)
Run Homebrew and select MAME, turn Wiimote sideways and up and down to select, 2 to start game.
Home calls up the menu, and pressing 1+2 simultaneously should quit you back to homebrew channel.
Things still to do:
I cant get the aspect ratio to work properly, so vertical scrolling games are stretched to widescreen.
It has a habit of dumping out: hold the Wii power button for 5 secs to switch of then restart.
Find a forwarder to make it appear as a Wii channel
Find a version that will work from my HDD instead of the SD card
Not all roms work, MAME on PC is much more forgiving than this. But Nemesis on a 42" plasma TV is feckin' ACE!
Hope somebody else can get some use out of this, and maybe help me out with the screen stretch thing?