I just built a mapper 0 cartridge with 32K/8K EEPROMS soldered to it for my semester project, along with a parallel port eeprom programmer. I used a SMB+DH cart which is mapper 66, and even though it is set to horizontal mirroring, both mirroring modes work great..i tested kung-fu, ice hockey (both vertical mirroring), and of course SMB with no probs. According to the solar wars website, u swap pins 1 and 27 (27 is WE' on the 28 pin eeproms im using) and that's it.