what do I upgrade? (512MB to 1024MB ram makes no diffs)

I am making a lot of dvd movies from my camcorder. The encoding process
(from DV avi to Mpeg) takes a very long time. I would like to know what in
my PC I must upgrade so that this takes less time.

I have a Pentuim 4 - 2GHz (running at 2.4GHz) with 1024MB DDR 333. My
motherboard however only runs the memory at 266MHz. The increase from 512 to
1024MB ram did not seem to make any difference in the encoding speed.

I also have a 7200RPM Maxtor 160GB HD and I don't have any video editing
card.