From ZD Net Australia:
in brief Citrix used its thin client technology to demonstrate an Apple iPhone running Windows XP, at the recent Citrix Application Delivery Conference in Melbourne.
Windows XP, seen below running on the iPhone, was loaded using Citrix's thin client desktop software XenDesktop. Using the Citrix ICA client — a UNIX application that allows devices to access Windows sessions on a Citrix server — the presenter was able to run Windows on the iPhone via Wi-Fi.
Hit the link above to see screen shots of the client running. The iPhone’s native touch screen pinches and other controls work as well allowing you to zoom in on the thin client while running. Tres cool.