I installed the vNES emulator and a couple of ROMs on my 8700, and although the games load and play, it is really choppy, to the point where it is unplayable. I am really surprised by that since it should have enough resources to play, even running on top of Java.
If you're not feeling adventurous enough to load this on your own handheld, you can download and install the BlackBerry Java Development Environment v4.1
which includes device simulators. You'd use this program to convert the .jar to a .cod file anyway. You can just go to C:\Program Files\Research In Motion\BlackBerry JDE 4.1.0\simulator, load one of the handheld simulators using one of the .bat files, and then load the COD for vNES by going to File -> Load Java Program.