SDLMame on your Wii? I guess so, I'll let the news do the talking:

This is a wii-linux distribution that includes the emulator SDLMAME 0.125 compiled for PowerPC. This emulator is the result of the efforts of the MAME team MAME. The source code that was used for this distro was taken from the SDLMame project, kept updated by Olivier Galibert and R. Belmont, and with the colaborationcon of Sven Gothel, couriersud and Vas Crabb. The original code can be found here:

http://rbelmont.mameworld.info/?page_id=163

Also, this distribution uses the wii-linux kernel POC 0.4, that can be found on its original page:

http://www.gc-linux.org

Specifications
This distro uses
• Kernel 2.6.24 (wii-linux POC 0.4)
• 52MB of MEM2 for swap
• 100 MB of swap on the SDCard
  
  How to use
  SDLMAME will let you play roms from old arcade systems. Here is the basic configuration, but it can be change by the user whenever he wants:
  
  CONTROLS
• [Grey ANALOG/DIGITAL PAD] Move the characters and handle the menu options
• [A] Button 1 / Select a rom
• [b] Button 2
• [Y] Button 3
• [X] Button 4
• [L] Button 5
• [R] Button 6
• [Z] ESCAPE (CANCEL)/(EXIT)
• [START] Pause/Options menu
• [YELLOW Analog UP] Coin PLAYER 1
• [YELLOW Analog DOWN] START PLAYER 1
• [YELLOW Analog LEFT] SAVE STATE //DONTīT USE
• [YELLOW Analog RIGHT] LOAD STATE //DONīT USE
  
  INSTALLATION
  To play with this emulator, you need a Wii homebrew enabled console (Twilight hack or Homebrew Channel).
  And you will an SDCard.
  
  To install this version of SDLMame:
• Copy the files "boot.elf" and "mamefs-fs to the root directory of your sdcard.
• Copy the directory mame and its contents to the root directory of your sdcard.
• Create a dyrectory called "mameroms" on the root of your SDCard
  
  To play with this game:
• Insert the SDCard on the front SD adapter of your wii.
• On your wii, execute the file "root.elf" using your favourite method for loading aplications (Twilight hack or homebrew channel).
  
  KNOWN PROBLEMS
• Loading times VERY HIGH:
• For little roms (2-4MB, CPS1) can take 3-5 minute in loading
• For big roms (13-20MB, CPS2,NEOGEO) It can take 30-60 minutes in loading
  After the loading part, it plays at normal speed (85-90% of original speed without frameskip and without lags)
• No keyboard or wii joystick support
• Problems using TV in 480p or rgb components
  
  Missing things
• Solve the gamesave option, in order tbe able to select a new savegame.
• Add keyboard/wii joystick
  
  Thanks to:
• Olivier Galibert ,R. Belmont,Sven Gothel, couriersud , Vas Crabb and ALL the MAME team
• All the gc-linux team

Download from the following rapidshare links binary, source and you can discuss it in the release thread at DCEmu.co.uk.