So, NASA's plans as far as Manned exploration is roughly have crew on the Moon by around 2020 and crew on Mars by 2030.

So if NASA gets crew on the Moon by 2020, that will mean it took NASA about 16 years to plan and execute this program and will have 10 years thereafter to get crew to Mars. And to do all of this within a normal level NASA budget- basically a inflation adjusted budget with no doubt various supplemental add ons due to overruns in projected costs [similar to NASA's past budgetary history].

Now, it's possible that within the 2008 to 2030 period significant increases to NASA's budget could occur and these increases could speed up this timeline, but that is somewhat irrelevant.

A point wish to make is that doing a manned mission to Mars is going to be difficult to do successfully. And because going to the Moon is easier than Mars, on that basis alone it makes sense to going to the Moon first.

Back in the early 1960's a reason for landing a man on the Moon, before the Soviets [the Apollo program] was because it was harder to do than build a space station in LEO. In other words such a task as landing a man on the Moon, required more time and effort and therefore gave us more time for us to "catch up" with the Soviets.
So, we beat the Soviets to the Moon, and thereafter walked backwards: build a space station [Skylab] then built a Shuttle, and then build ISS. Whereas a more reasonable seeming approach [something an engineer would envision] would have been: build a shuttle, then a space station, then the Moon, and then going to Mars and elsewhere.

Sending humans to Mars is a hard thing to do- though Mars fans will say it's not as hard as you think it is [and it's Earthlike, etc]. Going to the Moon is like riding a bicycle 100 miles and going to Mars is like riding a bicycle 1000 miles- going to Mars is about 10 times harder.

The point of me saying this, is not to argue against going to Mars, but rather to point out the obvious that after going to Moon [2020], we going to have less time than the time it took to go to the Moon. So we can't repeat the dance, of going to the Moon [Apollo], stop, then do Skylab, stop, Shuttle, stop, then ISS, stop. But rather going to the Mars has to be integrated into going to the Moon.
Now, this is actually NASA's plan as far as I understand it, but just because it's a plan doesn't mean they can't mess it up- and getting bogged down on the Moon is precisely one way of messing up it up.
And as for as PR the "This is a small step for man giant leap of mankind" message of the 2020 manned Moon, should be "This is the first step of human exploration of Mars".
And btw, I also think the highest priority of exploration of Mars should also be to also find minable water. Rather than the highest being to find signs of life.