How many atoms is 20-40 amino acids?
I took a quick look and saw that many of the SMP projects have over 120,000 atoms and there were other folding projects with over 300,000 atoms. There are also quite a few smaller folding projects (such as those run by the PS3s) with under 1000 atoms. # of atoms & description found at http://fah-web.stanford.edu/psummary.html
Can look at projects in 3D at http://jmol.sourceforge.net/fah/