For starters, if you are just using standard XP (not 64-bit) It won’t even come close to utilizing all that RAM. A good first step is to use the 3GB switch in Windows, which allows the system to recognize up to 3GB RAM instead of just 2GB. You can read up on how to do this here:
https://www.microsoft.com/whdc/system/platform/server/PAE/PAEmem.mspx
Aside from that, there’s not much you can do to optimize it aside from adhering to best practices – keep the pixel dimensions of imported elements below 2500x2500px, use a separate hard drive for your project media and, if you haven’t already, go into your After Effects preferences > Memory settings and make sure Disk Cache is turned on (and pointing at the media drive, NOT your boot drive).
Brendan Coots
Splitvision Digital
http://www.splitvisiondigital.com