There are a lot of variables to consider in addition to RAM. Specs on hard drive transfer rates, video cards, etc. Location of source file, location of premiere files (same hard drive or separate?).
You could have a top-of-the line processor and 2 GB of RAM, but if you're using an old IDE harddrive with outdated transfer rates, you've essentially bottlenecked your performance. How much virtual memory do you allocate?
Here's a suggestion, open up Task Manager and observe the performance window while you render/encode video in Premiere. This does take up some resources, but will give you an idea if your memory is sufficient.
Without knowing anything about your system, my guess is you would be better off upgrading to RAID harddrives than upgrading to 2 GB of RAM, but I've been wrong before.
