We can't find any reliable sources for this specific rumor, but it just won't die. Tying in with that rumor of Zac Efron proposing to Vanessa Hudgens while the couple was in Japan promoting High School Musical 3: Senior Year in January. Now, apparently the couple has set a wedding date for September 2009.
We still don't believe any of it, but it is weird that niether Zac nor Vanessa have denied the widespread rumors.