hardware acceleration or mobo/cpu/ram tradeoffs?

Hi,

I use ffmpeg on Knoppmyth to convert from MPEG2 created by a  
Hauppauge PVR-500 to mpeg4 divx with (using a myth2ipod script  from  
here:  http://www.myth2ipod.com/ that I've tweaked just a little.

It uses these options:

-y -cropleft 10 -cropright 10 -croptop 8 -cropbottom 8 -deinterlace - 
vcodec xvid -s 320x240 -r 29.97 -b 384 -qmin 2 -qmax 5 -bufsize 4096 - 
acodec aac -ab 96 -g 300

Currently this works great but is pretty slow, because I'm running a  
Celeron 700Mhz with about 128 MB of slow ram. (yes, I know)

My questions are:

a) are there any PCI or GPU boards that ffmpeg can use to do hardware  
accelerated conversions like MPEG2 to MPEG4 (divx or H.264)?  (I've  
looked up the new Nvidia boards but I'm confused as to their  
capabilities in this regard and on linux in general, and XvMC seems  
to be only for playback, right?)

b) if the answer is no, or yes but they are really expensive, then  
I'll be buying a new MoBo/CPU combo, so is there any set-up (type of  
MoBo or type of CPU) that works best for such a task?  Should I focus  
on memory speed/bus speed?  Anywhere I can learn about the trade off  
between RAM and CPU speed?

Thanks,
James