I'm one of those guys who's learned the hard way not to trust birth control. From my experience the chances are damned good. I often wonder if when they give a birth control a rating of 98% effective, if what it really means is that 98% of the people using will experience 100% effectiveness and that the other 2% of people (my category) get zero.
I've seen condoms, the pill, an IUD, and Norplant all fail in my personal life. Apparently I should have worn a Kryptonite jockstrap to negate the little wigglers.
There's a lot to be said for waiting to have a baby until you're "ready", but if the choice is taken away from you rest assured the wonder of fatherhood won't be one bit diminished.