According to unnamed developers cited by IGN, Nintendo's unreleased handheld 3D system, the Nintendo 3DS, is more powerful than the Wii, with "abilities" that are closer to the PS3 and 360.
Here's the quote:
"Several developers that have experienced 3DS in its current form have reported, off the record, that it has processing capabilities that far exceed the Nintendo Wii and bring the device with abilities that are close to HD consoles such as PlayStation 3 and Xbox 360."
Although no system info is available on the 3DS, IGN points out that the ability to render 3D requires that visuals be "drawn" twice (once for each eye), and that kind of thing takes significant processing power -- the PCs that run 3D games tend to be huge, expensive-looking boxes, so it will be interesting to see how Nintendo is able to cram that into a tiny DS.
Right now, not much is known about the 3DS. We don't know how it works, what it looks like, what it will cost, and only have a release window as opposed to a date. If Nintendo hits its announce mark, it should be out by March 2011.