How do you hide objects?
Also, how do I flatten them to a certain axis?
Are you using 2.65 or 2.49?
in 2.65 hit h to hide objects and alt h to unhide them (note this hides them from view and wont stop them from exporting if you have it set to export everything)
I believe you can also find it in the object menu if you go all the way up, hover of the the little arrow and let the menu slide all the way to the top, itll be up there.
Flatten an object on a certain axis? Do you mean Scaling it down to 0? Hit scale (s) the the axis name (x,y, or z) and then 0