Emulator to slow down the speed

In Emulators / NES ROMs

Does anybody know an emulator where I can slow down the speed very much, so that for example I can watch one frame for at least two seconds? It would be even better if the emulator could stop the whole game and move it on frame by frame whenever I press a certain key.
The reason why I need this is: I want to see every detail of the transformation scene when Mario becomes Super Mario and there everything goes very fast, so I need to slow it down that much. Unfortunately NESticle can just slow down up to 1/6 and FCE Ultra doesn't have this option at all.

I don't know about emulators that let you make a game so slow, but there's another method I could think of.
Record a video (some emulators let you make an .avi video, or use some software like fraps) and then watch the video frame by frame. There should be lots of videoplayers that can do that (perhaps...).

ha, I JUST found out something on accident today that will help you. In VirtuaNES, record what it is that you want to see by making a movie(in your case the mario transformation). Now, play back that movie. When it gets close to where you want to see, hit the Space bar on your keyboard. It will go one frame at a time with each keypress. I don't know how to make it start playing normally again from there, so I can't help you with that... I'm not even sure if there is a way to actually. Hope that helps.

Thank you very much. Exactly what I needed.

A touch late, but FCEU has been altered to support frame advance, among other things:

It works much in the same way virtuanes does. I think the default key for frame advance is the backslash, but you can change that as well as any other hotkey, which I find useful.