First steps with opencv and visual studio - c++

Question

i'm starting using opencv with visual studio, these are my sw components and environment:
windows 8.1 (64bit)
visual studio professional 2013
opencv 2.4.9
first of all i've downloaded opencv and extracted all in "C:\OpenCV-2.4.9", then i've created a new environment variable (user variable) OPENCV_DIR with value "C:\OpenCV-2.4.9\opencv\build" and added the string ";%OPENCV_DIR%\x86\vc12\bin" to the existing environment variable Path.
first question: do i should set x64 instead of x86 in the above string value? in general, are all settings right?
then i've created a new win32 console project with visual studio, it creates a function _tmain(int argc, _TCHAR* argv[])inside a .cpp file named .cpp.
second question: what is the reason because i've to use such '_tmain' function instead the classic 'main' function? which is the structure of the calls when i 'run' the project? is that useful? and if i wish use the classic 'main'?
then, i've defined the following code
int main(int argc, char* argv[])
{
if (argc != 2)
{
cout << " Usage: display_image ImageToLoadAndDisplay" << endl;
return -1;
}
Mat image;
image = imread(argv[1], IMREAD_COLOR); // Read the file
if (image.empty()) // Check for invalid input
{
cout << "Could not open or find the image" << std::endl;
return -2;
}
namedWindow("Display window", WINDOW_AUTOSIZE); // Create a window for display.
imshow("Display window", image); // Show our image inside it.
waitKey(0); // Wait for a keystroke in the window
return 0;
}
when i compile and debug with visual studio everything is ok! but i cannot be able to give the requested parameter to the function... it starts and ends with output code -1 (the first if check).
moreover, if i find the .exe and try to run it using the prompt, an error occurs:
"Impossible to run the program because opencv_core249d.dll is not present...... try to reinstall the program".
it is clear that these are common problems but i'm finding these issue so hard... thanks to all!