Purchase an iPAQ hx2110, hx2410, hx2415, hx2750 or hx2755 running Windows Mobile 2003 SE between August 28 and December 31, 2005 adnd HP will give you a free Windows Mobile 5.0 Upgrade CD. There is no word yet on when the upgrades will begin to ship but they are expected shortly.
Not surprisingly given that the upgrade for the hx4700 has been delayed till next spring, the rebate does not cover the iPAQ hx4700.