See this page for information and recommendations about memory and improving performance in After Effects.
Recommendations in general are difficult because every composition and computer are different, as are people's preferences regarding rendering speed versus length of RAM previews, what other software they want to run at the same time, et cetera.
But, I'll make a very broad recommendation:
For HD-sized movies, you want to have 3-4GB of RAM installed per processor. So, for a quad-core with hyperthreading (which effectively has eight processors), you'd want 24-32GB of RAM. This describes my personal computer, by the way, so you know that I have put my personal money where my recommendations are.
Don't neglect hard disks. You need to have more than one hard disk. Sooooo many people complain of poor performance and fret about RAM and CPUs, and then I find that they're running their OS and applications from the same single disk that they're reading source files from and writing output files to... or their external disks are over a USB connection. [*shudder*]
BTW, particle effects like Trapcode Particular take a long time to render. That's just a fact of life. You may make them faster, but you'll never make them fast.
Thank You. So I should be OK with a Quad core MAC PRO with hyper threading, (Westmere i guess) with 32 MB of RAM? May I ask how to set up the additional disc? I am only using one disc, the one on my computer.
> So I should be OK with a Quad core MAC PRO with hyper threading, (Westmere i guess) with 32 MB of RAM?
Assuming that you meant 'GB', not 'MB', yes.
> May I ask how to set up the additional disc? I am only using one disc, the one on my computer.
Get a computer with two internal disk drives (or better, three). Install OS and applications on one. Have source files on another. Have output written to another.
There are a _lot_ of resources for optimizing for performance here. Please go through those and then ask questions if you still have any.