Yes my laptop has 4 GB of ram. I once tried to simulate a ramjet without combustion on a dual core desktop with 2GB. It really needed about 8GB of ram for the simulation and started swapping like crazy. At that point every 4k of ram I could free up helped. I even resorted to using some of my video card memory for a fast swap file. It helped some when I off loaded some of the processing load to a single core machine with just 1GB but still it was too slow and I gave up.
You really don't want to swap at all when you simulate so the more ram you have free the better. There is another new kernel feature that uses some of your ram as a compressed swap file that may help as it is less costly to compress and decompress from ram than to swap out to disk but it is still experimental with some quirks.
compcache - Project Hosting on Google Code
I'm still no expert at this but often you can't have enough hardware to throw at serious problems. Another part where you'll need a lot of ram is when it comes time to visualize the data.