Unfortunately, emulating SNES on the DS is kind of pushing it. It has 99MHz of power (total, but the fact that there are two separate processors, it makes it hard to use it all) and the SNES goes at 21.5~MHz. Plus, the fact that many games have special chips that require extra emulation, and games range from 512KB to 4MB in size, and the DS has 4MB of ram to use, so there is paging for larger games. Plus, I'm not sure the DS is truly capable of Dynarec, which would normally be an easy ticket out. The PSP has 333MHz maximum, plus 32MB of RAM for phat and 64MB of RAM for slim. Also, the PSP has more capability at it's disposal.
So basically, Super Mario World and most of the early, low power, no special chip games will be all that we could pull off on the DS. There's not enough power to really g crazy here. I would have to say though, the DSi may have some hardware that may become accessible (with proper study) that could make it a little easier, but I would get your hopes up.