Go up in the attic. If the wall runs in the same direction as the ceiling joists, it's not likely to be load bearing -- highly unlikely, in fact. If the ceiling joists run perpendicular to the wall, it is probably load bearing.
I would still put a header in, even if it is not load bearing. It will give you a more solid wall. If you have the tools, and the skills, by all means do it yourself.
Make sure you poke holes in the wall first, to check for wires that you may not know are there. If you cut into one, it will ruin your day, at the least.
CD