increase system performance - how to?

[BabaG]

i'm looking to process timelapse sequences of raw images. the tests i've
done so far work well but are very slow. my main experience is in audio
and video editing so i'm a bit uncertain as to how to optimize a system
for still image processing. which of these areas would have the greatest
impact on efficiency in an nconvert workflow?

processor speed
bus speed
hard drive speed
memory speed
amount of memory

my guess is that it's the processor speed but the loading of the image
seems to be a point where things bog down. that's why i include bus
speed and hard drive speed.

tests are being done on an inexpensive compaq sempron 3400+ system
with 1gb memory. would love to get something 4-8 times faster but not
sure how to go about it while getting the most bang for the buck.
suggestions please?

thanks,
BabaG