Your central processor is the bottleneck, not the amount of memory. To see how the process priority setting affects the priority of each thread, you can use an older version of
TaskInfo. Try ffdshow as a decoder for all video formats. It's fast, allows flexible configuration and chances are it will the right priority for your system. :) With a computer like that you should uninstall all non-essential background programs, such as an antivirus. It will also free up memory for hungry P2P servers like eMule. But before you change the configuration of your system, you should check which programs are using most CPU resources.