Select Show Details from the pop-up menu to see OmniPlan's print options.
You can print the task view or the resource view, whichever one is open in the main window. You can then choose whether to print the outline, the chart, or both.
Or, you can choose to print an HTML report of the project. This works just like exporting to a web page, and uses the same HTML templates.
The dimensions are calculated based on the size of the project and the scale set in the Page Setup dialog. When you change the width or height, the other one changes accordingly. Note that this overrides the Scale setting in the Page Setup dialog.
You can use the Cropping settings to chop off any part of the project you don't need. An overview of your project is here. To define the area to print, resize the cropping box by draging its left or right edge, or move the box by draging its center. If you enter dates in the From and To fields, the cropping box updates to match.
The preview shows what your project will look like on paper. Use the buttons to step through the pages and get an idea of the scale and layout.
Note that like in any application that uses the Mac OS X printing system, you can "print" to a PDF file instead of to real paper.