I'll come from a perspective that I am fairly informed but I don't know everything position.
1) Why you would vote for one over the other. McCain or Obama?
Obama. More down to earth, actually focusing on the 90% of America that is hurting from current economic problems. His foreign policy isn't perfect, but considering the alternative, McCain, I'll stick with Obama to not get into another war (unless we get attacked by a real sovereign state). Policy wise, Obama has some good ideas, but it will be tested the day he gets into office and actually gets them passed (or at least discussed); the same thing goes for McCain.
Jokingly, I'll be surprised if McCain makes it to Election Day =P
2) Who do you think is the stronger Vice-President Candidate?
I don't know enough about either, but from what I heard from the media, Biden seems like the better choices of the two.
3) Do you believe the current economic tensions in the financial and stock markets will affect the voters?
The last 9-10 months already showed, stressed out, and pissed off all voters how our economic system needs fixing if not borderline overhaul. The US dollar has lost at least 20% face value and while everyone else in the world is coming here to buy cheap US goods, it does affect other people relying on the strong US dollar to help immigrants support their families (example - Mexicans sending US money to help their family back in Mexico, Filipinos in the US and other places sending US money back to the Philippines).
Now if we didn't invest in Iraq, 700 Billion USD won't sound as bad right and we can shrug it off, but that is another story.
4) Is high gas prices/energy still a concern? Will it affect the election?
Still is, will be still by Election Day. When I graduated high school back in 2002, gas was maybe 1.60-1.75. We peaked at 5+ and though we're dropping, I don't think we'll ever see very low gas unless we GTFO (replace the O of out with off) oil. This dependence on oil is hurting us and the current Bush administration barely gave money to alternatives.
Sorry that I had to use GTFO in a wierd context, but if you look at it, its what's been the thing for the last eight years...