Is it possible to use two macs power to do one process?

Possible yes, and it is something studios do using banks of cheap linux machines and really high speed network connections.

For somebody in the home, not so much ... unless you want to write your own software.

Likely getting a newer copy of the SW that wrangles the GPU into the conversion process under Snow Leopard might be a better option.

 

Yes, however that is usually a professional feature that costs alot.

Since your budget seems very low (iBook), it's better to look into an intel mac.

Some software does it with xGrid, some software does it using custom software.

 

I assume you're converting a ripped DVD to h.264. If that's the case get an Elgato Turbo.264. It'll convert in near real time and won't cook your iBook. I consider it a must have if you want to convert on an older machine (it works well on Intel Macs too).

 

Visual Hub could use xgrid, but unfortunately it's not available anymore.