After having an H1-B approval, can one start working before Oct 01, 2006?

[aquashash]

My wife is currently with me in US on an H4. I plan to apply for her H1-B this April 2006. If I do manage to get her H1-B approval within a month under the fast track program, can she start working immediately? Or does she have to wait till October 1st, 2006?
Can someone please answer my query?

Thanks in advance.