How can I speed up or slow down old 3D games?

Solution 1:

For some games, the single best way to cause artifical slowdowns is recording using FRAPS or equivalents. Since the encoding burden is mostly constant frame by frame, it more or less causes an uniform delay on the game.

Solution 2:

I've found a solution:

http://www.asoftech.com/as/index.html

It isn't free, but really slow down the game. I've tested with desmume emulator + pokemon white rom, and the game speed really changed. I don't know if it really speed up, but slow it does. :)

Now, I know that is possible, I can try develop myself or search free alternatives.