According to BMI's Diamond Club news:
"...EgyptAir – who have routes across Africa, Asia, Europe, North America and Australia – [will] join the Star Alliance network on 11 July 2008."
Another article confirms the July 11, 2008 date. EgyptAir already has a plane with the Star Alliance livery.
This date comes as a bit of a surprise as last October when EgyptAir's pending admission to the Star Alliance was announced it sounded like it might take 18 months for EgyptAir to gain membership.
Members of Star Alliance frequent flyer programs should be able to look forward to redeeming their miles for EgyptAir flights and earning miles in their local program when flying EgyptAir starting on July 11, 2008.