The Atari 7800 and Colecovision are considered to be in the same gen as the Atari VCS / 2600, but they could emulate its games.

The Cell contains ONE ~3GHz PPC core, Wii has ONE ~700MHz PPC core, XB360 has THREE ~3GHz PPC cores, so, as far as CPU matters, Wii emulation should not be impossible, while emulating the two other PPC cores using SPEs AND obtaining the power of two 3GHz ones wouldn't be easy at all. In the glorious DEC Alpha times, DEC was able to emulate a 200MHz 486 with a 500MHz Alpha (that had several times the computing power of an hypothetic 486 equally clocked), but Alpha was a general purpose CPU, while SPE is a special purpose one, so it would struggle a lot more to emulate a GP one, despite being Turing complete. It's quite unlikely that six of them could deliver the emulation of two PPC cores at roughly their same clock. So XB360 emulation, if possible, wouldn't deliver enough performance to run games smoothly, although it could be used for study and reasearch, development and mere curiosity purposes.

No.

The rendering is managed by the game code (that's why ps3 or xbox360 games have different rendering resolution), not the (WIii/ps3/xbox360/pc...) OS or hardware, so the emulator can only upscale and add filters to the upscaled image (rendered in native resolution, that is 480p). You can add AA, because that's a post processing operation, but you can't change the rendering resolution.

Cell one PPC Core

Wii one PPC Core

"while emulating the two other PPC cores using SPEs AND obtaining the power of two 3GHz ones wouldn't be easy at all."

?

What two other PPC Cores ? Are there any ? Are you talking about the PS3 emulating the 360 ? 

Yes, someone after the OP suggested XB360 too (*), I was pointing out the differences: qualitatively there shouldn't be any in theory, only quantitatively, but the fact that PS3's Cell has only one PPC core and XB360 three makes the difference qualitative too, as to try to get the same CPU performance would mean needing to emulate the other two XB360 PPC cores using SPEs. OTOH an emulation not working at full speed, only for study, research and development, should be possible.

(*) I notice now that I wasn't clear enough, I mentioned XB360, but when I wrote about the "two other PPC cores" I didn't specify I was talking about XB, and I mentioned Wii in the previous clause, it was quite ambiguous, sorry.

Okay.
Emulations requires more horsepower than the original system.
Possible? Sure. Full speed? Doubtful.

GameCube was more powerful than the first xBox, thanks to its PowerPC CPU (look it up)

HD is a resolution, games aren't defined as HD by their lighting and shading.

You can't compare "ur mhz and ghz and ram" numbers on consoles, its more about the processor itself then the little number on the side.

In theory the PS3 is more than powerful enough to emulate a Wii and the PS2. However to recreate an emulator on the PS3 is a difficult task (if want to go for full potential). For example emulators on the PC would require a lot of redesign to make good use of the Cell's SPUs.

If the emulator can only run on the 3.2 Ghz PPU, you're not using the 7 other 3.2 PS3 Ghz processors which are just as powerful.

Those official gen classifications are pretty useless. The Colecovision from a hardware perspective was a new gen console compared to the Atari 2600.

Also the Colecovision did not emulate Atari 2600 games, basically an expansion module included all of the Atari 2600's technology. Basically you added an Atari 2600 clone as an expansion.

The games generally use the libraries (part of the SDK) provided by Nintendo/Sony/MS instead of programming to the bare hardware. Modern emulator tend to work by emulating said libraries. It is called HLE for high level emulation, as opposed to emulating the hardware itself (which is now dubbed LLE for contrast with HLE). 

When emulating hardware you indeed cannot render at a higher resolution but can only apply post-processing effects but when using HLE you are replacing a big part of the software stack with your own software so that if (and it is quite likely) the game uses the manufacturer's graphic libraries then the emulator's own graphic libraries are used instead, which allows it to render at a higher resolution (of course the assets themselves are at the same level of detail and have to be "upscaled").

....I mainly do ps3 and pc man.....

Take the goggles off because everything you just said was wrong.....

1. Emulation depends on system architechture and CPU. The ps2 runs off of a chip called the emotion engine which ran competly differently then from the cell. There were also two forms of emulation. Direct softmod or an emotionchip installed. With the softmod all power runs off of the cpu. This takes a lot more power a cpu then it normally would if achitecture was alright. Seeing how no one really knows what the cell can do just yet, I don't know how many ps2 games it could run at once, but knowing how most emulation runs...probably just 1. If you're running the emotion chip emulation then that runs off of gpu instead. Ps3's gpu is only twice as strong....you can run about 2 ps2 games at once.

2. Yes....Yes you are.

3. The feature was built just fine considering how hard it is for different archtectures to emulated. Also it looked perfect if you used a standard definition tv and even had updates that helped the soft mods get pretty much every ps2 game compatible....we would have liked upscalling for higher def tv's though.

4. For the emotion chip cells....yes this is understandable, but for there soft mods....there was no added costs. So you're only half right

5. What in the bloody hell are you smoking!