To just interleave and nothing else, try this:
clip = avisource("yourclip.avi")
even = selecteven(clip).selectodd
odd = selectodd(clip).selectodd
interleave(even, odd)

There’s definitely some antialias filtering applied to the second shot. Try processing this, which doesn’t apply any filters:
avisource("yourclip.avi")
If it still looks antialiased, there’s might be some problem with virtualdub’s settings.

Original video: http://img707.imageshack.us/img707/8319/uncompressed.png

Interleaved: http://img860.imageshack.us/img860/3039/interleaved.png

Not only it cuts beginning of video a bit, it also lowers quality. Also, how do I not fade to black with that script?

The specifics depend on your software but you can apply any filter and tell it to output the result without compression. For example with avisynth + virtualdub, you load the avs file and set it to “direct stream copy” in the video menu.

Of course you are losing half the frames so it’s compressed in that sense.

If it looks OK cut down to 30 you shouldn’t need to do anything. New games with their 3D graphics don’t generally rely on framerate gimmicks like flickering.

If 30 fps takes away something important, try merging and interleaving and decide which one looks best. If it makes something else screwy, like the renda punches and kicks, you can apply the filter only to the appropriate parts of the clip and apply a flat half rate to the other parts.

One question though, is this problem also responsible for things like SFIII Yun’s Genei Jin shadows not appearing? Or is that a separate frustrating problem? :D