Which program(s) to use for multi core CPU support?

[Ice =A=]

At the moment I use DVDx for converting DVDs to XviD. Since I'm about to buy an Athlon X2, I'd like to know if dual core CPUs will improve encoding time automatically encoding with XviD. Or are there any special programs (like DVDx, AutoGK, virtualdup) which use the second processor core? Which one would you suggest?
Thanks a lot!

Edit:
I understand there can be multi core optimizations in the codec and in the encoding program you use, and so far XviD has no such optimizations. Will there be a special Xvid-multicore-version in the near future?!?

[berrinam]

I don't know about XviD, but x264 already has multi-core optimizations.

[sysKin]

I understand there can be multi core optimizations in the codec and in the encoding program you use, and so far XviD has no such optimizations. Will there be a special Xvid-multicore-version in the near future?!?
Yes please find a person who can code such thing, and I can provide information which part, exactly, can be multithreaded - without changing the bitstream at all. I have this idea and it's quite interesting, too bad I have no time to implement it (and no motivation, other than "fun", because I have one core and I don't use xvid anymore anyway).