All are moddable. Just the newer ones that have a D2C chip have to use the D2CKEY , which is 31 wires compared to the older chips which are 5 or 6 (Can't remember).
You can find out what your wii has by either opening and having a look to see whats printed on the chip (D2C , D2B etc) or there is a website that you can put your serial into and it will give you an idea of what should be there. Can't remember the site though , so you'll have to search or wait for someone who knows it.