Okay, so NO "Prequel Trilogy DVD box set" that we know of. Just an "entire saga ultimate set" coming out May 2007.
And SW.com makes it sound like this is the "one and only" time that the "theatrical versions" of the Classic Trilogy are coming to DVD (promises, promises!). So presumably the "Ultimate Saga Box Set" (or whatever they decide to call it) coming out in 9 months will only contain further tweaked versions of the classic trilogy, tweaked Episode I and no idea about Episode II and III. They theorize a "bonus disc" of Original Trilogy extras like deleted scenes, but I'll believe it when I see it.
Of course now LucasFilm could always get around their "promise" by releasing the "original original trilogy" on next generation format like BluRay/HD-DVD, but that's pure speculation at this point.
Currently their story is Sept 12-Dec 31st 2006 will be our "last chance" to own the "unaltered" Original Trilogy on DVD format.
Right now I'd say there is no reason to wait, just buy the version you like best (you get them both in this new set). If you want to wait, there will surely be some copies on ebay when you want them (though who knows about the price, they may be cheap or they may be expensive, but I doubt they would be that much more than the suggested retail price).
Don't bother wasting your money on a new set of modified movies hoping that you'll like whatever changes he has in store. He will never be satisfied with these movies, and will keep tinkering with them as long as he has life, breath and the money to do so. If you're really curious, you can always rent them from Blockbuster or Netflix to give 'em the "once over" and see Greedo fall on his own blaster, Amidala's ghost hugging Hayden at the end of ROTJ while the Ewoks dance to N'Sync with dj M.C. Binks or whatever else he plans to do to these movies yet...