Advice on a building a workstation

I am putting together a Windows 7 workstation for a friend who will be doing a lot of design work using Photoshop, Illustrator, Publisher and some sign design applications, including Flexi10. While none of these is particularly resource intensive, he does deal with very large files. He wants 16 GB RAM at least. The Flexi10 program requirements does say it needs 4GB of working disk...