On the higher and lower ends of the spectrum: For me 16BG RAM, 3.2 GHz processing and Intel 2GB RAM, 1.33Ghz both worked fine on two different laptops.
Depends on how long you like to sit around and twiddle your thumbs when you run the project. :) Get the fastest machine your money will buy. SSD's help a TON. Seconded by Processor speed and cores (multi-threaded), healthy bit of ram but 4gb is acceptable. But the I/O on the HDD is why the SSD will benefit you the most.