So what exactly does NASA need help with?
Specifically, NASA is looking for help with:
(1) The ARES Science Team.
(2) ARES Education and Public Outreach (E/PO) Team.
(3) Design and development of the aerial platform structures and mechanisms subsystem including the composite airframe, associated hinging and latching mechanisms, and control surfaces.
(4) Design and development of the liquid rocket propulsion subsystem for the aerial platform.
(5) Design and development of the command and data handling, flight software, and the navigation sensors (only for entry and flight over Mars).
(6) Design and development of the telecommunications subsystem for the aerial platform and entry system.
(7) Design and development of two complete cameras.
Or as far as we can see, NASA would like someone else to help with pretty much everything except the spacecraft and aeroshell bits, presumably fairly closely modelled on those used in previous Mars lander missions.
That said, the space agency has evidently made its mind up about propulsion, plumping firmly for the bipropellant rocket. According to this pdf other options were considered - fuel cells, batteries, different kinds of combustion engines. Though some offered greater range and/or endurance, they were mostly assessed as requiring massive development effort (especially on propellers able to operate in the thin atmosphere of Mars) and associated risks of failure.
One thing which doesn't seem to have been considered is the use of nuclear power, though NASA has specifically stated that Advanced Stirling Radioisotope Generators (ASRGs) can be used in Discovery missions - another candidate, the proposed robot windjammer intended to sail the patio-gas seas of Titan, moon of Saturn, will employ an ASRG.
There is 63kg available in the ARES airframe for fuel and propulsion: this could permit three ASRGs to be carried, offering 450 watts of output. That's not much power - a bit over half a horsepower - but on the other hand the ARES apparently requires just 40 newtons' poke to push it along, a mere 8 or 9 pounds of thrust in Earthly terms. Model aircraft in Earth's atmosphere can achieve 3 or 4 pounds of thrust at 3-400 watts. Perhaps the bigwigs of NASA could do better, especially as it might be possible to lighten the ASRGs by removing some or all of the electric generator hardware.
If it were possible, that would mean an ARES sky-cruiser able to fly for as long as 14 years rather than just 70 minutes or so, and prowl much of the surface of the fourth planet. This kind of long endurance and (relatively) high power output is the reason that the planned "Curiosity"/Mars Science Laboratory ground rover - to feature a laser capable of vaporising rock - is also to be nuclear powered.
That's speculation, however, and the NASA studies to date make it clear that they've decided on the tried-and-true bipropellant option. It may not even be possible to design a propeller to work in the thin atmosphere of Mars, or not until more is known about it.
The ARES Mars-plane is still a pretty exciting idea, though, even with flight endurance of only an hour. If we had a vote, we'd be voting for it to make the Discovery cut.