As of right now, intrade.com reports a 7.4 percent probability that Hillary Clinton will get the Democratic nomination for President -- and an 8.0 percent probability that she will be the next President.
That seems a bit unlikely to me.
Intrade isn't an efficient market; there are tons of arbitrage opportunities like this. (Some are more subtle.)
Although if you want to get technical, buying Clinton getting the Democratic nomination (at 74 cents for a contract that pays $10) and selling Clinton winning the '08 election (at 80 cents) isn't quite risk-free -- there's a nonzero chance that she might want so badly to be President that she'd run as an independent in order to do so. And it's my understanding that short selling (which would be necessary to pull this off) isn't possible on Intrade anyway.