From this article on MGS aerobraking, the projected surface area was 17.04 square meters and an aerobraking mass of 745 KG. The article states that MGS started with an aggressive aerobraking schedule but encountered problems with the -Y solar array support mechanism. As a result, they lowered the dynamic pressure allowable on aerobraking passes to 1/3th the original value, with the new value being 0.2 N/m2 (3.408 N) at peak. That means the original dynamic force was 10.224 N at max Q. The new periapsis altitude was on the order of 117 to 122 km.

According to the Mars Odyssey aerobraking page, they'll be doing 380, not 780 drag passes over 78 days. The periapsis will be 120 km, so we can expect the dynamic pressure to be on the same order as that experienced by MGS, allowing for atmospheric fluctuations, of course.

From Mars 2001 Odyssey-Spacecraft, the vehicle had a launch weight of 725 KG, including 348.7 KG of propellants. It consumed a lot of that propellant doing the orbital insertion burn, so the vehicle's current weight is probably somewhere on the order of 500-550 KG, substancially less than MGS's aerobraking mass (yes, I know I'm using mass and weight loosely). I can't find the MO projected area, but since the aerobraking mass is less than MGS, it stands to reason the projected area is also less. I seem to recall, perhaps inaccurately, reading that MO's aerobraking area will be closer to 10 square meters. If so, then the peak aerobraking dynamic pressure would be on the order of 2 Newtons, with the average pressure being somewhere around 1 Newton.