First, you need SD card or SDHC card.
Press wii icon at the bottom left corner, press data management, and continue press the place where data management was located until you see all the saved game data what you just played before. Find the game icon you like to transfer. Next, press coppy or cut and press OK or yes not sure. It will paste into your SD or SDHC card. Now, bring your SD to your another wii and plug it in and turn it on. Go to the same place you just did at the previous wii, which is data management and press SD and you will see the game or games you just pasted from old wii.
Hope this works