Here's a great article on how to design wii friendly pages. 

Key Items from this article if you don't feel like reading it are:

1. The web pages are restricted to 800 pixels wide.
2. The opera browser supports flash 7.
3. It does allow for one popup window.
4. The opera browser's HTML, CSS, and scripting capabilities (including XMLHttpRequest/AJAX) are the same as Opera 9 for desktop.
5. Instead of reformatting the page to attempt to make it fit on the screen, Opera on Wii lays the page out as if it was using a virtual screen 800 pixels wide. The height of the virtual browser window changes depending on various settings, but can be between 376 and 660 pixels high.
6. As long as it is pointing at the television, it is a mouse. Wherever the user points the remote, the mouse cursor will point. When the user presses the A button, it is the same as clicking the left mouse button. When the remote stops pointing at the television, it becomes a minimal keyboard. Pressing the A button then is the same as pressing the Enter/Return key on a keyboard.
7. Scrolling the page is normally done with the trigger button. This works as a panner, in the same way as middle-clicking the mouse would work on desktop, except that it only scrolls as long as the user holds down the button.
Long page addresses take long to type. Addresses that mix uppercase and lowercase characters require additional key presses to enable or disable uppercase. Addresses that use accented characters are particularly laborious.
8. Long page addresses take long to type. Addresses that mix uppercase and lowercase characters require additional key presses to enable or disable uppercase. Addresses that use accented characters are particularly laborious.
9. As with CSS, JavaScript will see the virtual browser window size, not the actual television resolution: window.innerWidth, and similar properties, such as document.body.clientWidth, will all be 800. window.innerHeight and similar properties, such as document.body.clientHeight will all give the height of the virtual browser window. Properties such as screen.height cannot be used.
10. Opera on Wii has the same image capabilities as Opera on desktop. This includes JPEG, GIF, PNG (with alpha transparency), BMP, ICO, SVG 1.1 basic, and scripted canvas. If your images display correctly in Opera 9 on desktop, then they should also work on Wii. With plug-ins, however, there are some significant limitations. Only one plug-in is currently available for Wii, and that is the Adobe Flash Player 7 plug-in.

http://dev.opera.com/articles/view/making-wii-friendly-pages/