I make flowcharts in Word all the time. It offers me more flexibility than other programs written specifically for flowcharts.
Turn on your drawing toolbar.
Use text boxes for your boxes of text. If you want a shape other than rectangle, use the text box and make the line surrounding the box transparent. (right-click on the text box, choose properties, and change the line color)
Under the Auto-Shapes:Basic shapes menu you will find most of the unique shapes that you are looking for (such as diamonds, rectangles with rounded corners, etc.) Put them over the text box and change the properties (just like as above) to make the background transparent.
It’s good form to “group” these items together to be considered as one unit (draw menu, group option) before moving them around.
And of course the straight arrows can easily be found on the drawing toolbar. If you want a curved arrow, look under auto shapes: lines and choose the curved line. Make it curve the way you want to to, right-mouse click on it and choose properties, and you will see how to make an arrowhead on one end of the line.