No, but he doesn't deserve credit for it anyway. He also doesn't deserve to be second guessed on everything. For some people President Obama can do no right.
Apparently if you keep repeating something enough times, some people will believe it no matter how blatant a lie it is.
http://www.washingtonpost.com/wp-dyn/content/article/2008/09/09/AR2008090903727.html?nav=rss_print/asection
I'm afraid that's all it is, just a rumor. That would be an unbeatable duo though. Colin Powell is an amazing strategist and would be beneficial as a VP for either candidate. He hasn't been pleased with Bush and Co. for a number of years. I doubt very much that he will endorse Obama, but...