Is there any way to distribute x264 encoding jobs across multiple computers (to increase the encoding speed)?

You could render separate chunks of the video, and use VirtualDub to stitch it all together with its Copy mode (where it does no encoding). It's not real distributed encoding or anything, but simplest solutions sometimes work the best.

It's beta, but functional. It's not quite as straightforward, but it works. It IS windows based and free.

ELDER from some Doom9 guys

You could also try using this , its a parallel/distributed encoding software for windows and works well and scales nicely too.

Try googling for xcode Parallel encoder.

These links should provide more information.

http://superscalar.pbworks.com/