If your really serious you may want more ram. There are a few free and opensource CFD/FEA software packages for linux. The one I have played with is OpenFoam. Its not the most straight forward software but there are a lot of people doing really cool stuff with it.
http://www.opencfd.co.uk/openfoam/
http://openfoamwiki.net/index.php/Main_Page
http://openfoam.cfd-online.com/cgi-bin/forum/discus.cgi