How possible is it that I conceived in the early morning of Oct. 11, 2007 if the beginning of my last menstral cycle was Sept. 31, 2007

Definitely possible. The timing, if that is when you did conceive, suggests that the child will be a girl.

Ovulation occurs aprox. 12 - 16 days into your cycle (day 1 is the first day of your period)

September 30th to Oct. 11th is 12 days.