Sinexus - As far as I know, the gridlines are in 1" squares, so if you're working on a project that's not a perfect square, you'll never have gridlines that fit.
I think the easiest way to control a grid is to use the Rectangular Grid Tool. Create a new layer, name it and drag it to the lowest level. Choose the Rectangular Grid Tool (found under the Line Segment Tool) - double click it on the toolbar and adjust the options to suit your project. After you have your grid you can change the color and adjust it freely like any other vector object. When you're done, lock the layer and continue working on the other layers. Before you print just turn off that layer.
...kim