Hardware configurations for processing nonlinear Simulations and Flow Simulations at resolution levels 4 and higher.

Get a 64bit OS and 8Gb or more of RAM. That would be the minimum requirement.

Also, make sure you use best practices in meshing to reduce computing resources and time toll.

what kind of analysis are you doing? Sounds awfully laminar & non-Newtonian?. Is this typically a transient of steady state analysis? Do your goals go flat? You must have awfully intense geometry, yes? What other physics to you have going? What's the objective? Optimizing the mesh as Alin says can pay big dividends in cell counts and hence CPU time. Well worth the time you spend at it.

If you have it all buckled together, then get the fastest cpu you can afford (5600 series Xeon's (for a dual socket system) or the equivalent i7 for a single socket), a RAID 0 array or a largish SSD (kinda pricey) (not so key if you are doing steady state analysis), 12GB (min) or if dual socket mobo and CPU) go for 24 GB. Get an ATI fire pro V7800 - seems like the best value these days as far as I can tell at any rate. Not the most clear cut thing on the performance side (tough to find an apples to apples comparision for Quadro and ATI) but the price is pretty reasonable and compared to the Quadro's it is no contest. The BOXX guys have the over clocked systems but they are not that much faster than the non-over clocked due to, forget the name, for the Intel dynamic clock rate technology. But they might be just the ticket for long run analysis as the auto over clocking is thermally constrained.

Have to a a 64 bit OS - no question.

You might have all kinds of potential issues on the NL FEA stuff not finishing - do you contact? Solid elements? Dynamic, steady state?