Correction to AT's writeup: Immediately after the flop you have about a 31.5% chance of making that
straight. You've got eight cards out of 47 that can help you, but you've also got the
turn and the
river left, thus giving you two shots at making that straight.
The fact that the odds are close to one-third is critical. If more than two people (including you) are in the hand, then pot odds dictate that you should draw for your straight as long as the bets are reasonable. If you're heads-up against someone, however, then you're drawing for the chance of doubling your money when your odds of doing so are one in three.
Also, a four-card flush has a slightly greater chance of hitting, since there are nine outs to the flush, as opposed to eight for the straight.