Today is a big day for Most Powerful Women, as we at Fortune call women leaders. Today I had lunch at Google's (GOOG) New York offices with 33 rising-star women from around the world who are completing their month-long Fortune-U.S. State Department Mentoring program.

And tonight, these mentees--who have been shadowing top female execs at U.S.-based companies like American Express (AXP), Goldman Sachs (GS), Exxon Mobil (XOM) and Time Warner (TWX)--will join 100 other women at Fortune's Most Powerful Women Evening With... dinner at the Time Warner Center.

I'll be taking the stage with Christiane Amanpour, the renowned international correspondent who built her career at CNN is headed to ABC, and Anne Mulcahy, who ends her career at Xerox (XRX) today.

That's right. Mulcahy, who last decade turned Xerox around and last year turned over the CEO reins, today gave up the chairman title to Ursula Burns, her CEO successor. It's all quite historic since Burns is the Fortune 500's first black female CEO. Theirs was the first-ever woman-to-woman CEO hand-off in the ranks of America's largest corporations.

We'll talk tonight about Building a Legacy -- the theme of this year's Fortune Most Powerful Women Summit (October 4-6 in Washington, D.C.).

I checked the longevity charts and found out that Amanpour, at 52, and Mulcahy, at 57, both have more than a quarter of a century left to make their marks -- beyond the legacies they've built, that is. So, what's your next act, ladies?

Mulcahy will talk about her trip to India and Afghanistan -- she just got back to the U.S. For Save the Children, where she's now chairman, she also visited Haiti and Guatemala -- and wrote a Postcards Guest Post about one of her trips. Mulcahy also recently joined the boards of Johnson & Johnson (JNJ) and the Washington Post Company (WPO) -- while she's leaving the boards of Citigroup (C) as well as Xerox.

And Amanpour? She's departed CNN, where she was one of Ted Turner's first reporters, and is starting August 1 at ABC. She'll be taking over George Stephanopoulos' hosting spot on This Week on Sunday mornings. Amanpour's mission has long been to bring more international news to the American people. Think she can do that at ABC? I'll ask her tonight.

Stay tuned to Postcards for a report on tonight and more about Most Powerful Women.