You just want to screen a rectangle? That's easy enough.
If you're in PageMaker, draw your rectangle. Hit CTRL-J to bring up the color dialog. Apply the color you want to the rectangle, then change the tint to 10%.
In Illustrator, draw your rectangle. Select the stroke and set it to none. Select the fill, then open the "color" dialog. Apply the colour you want (it will have to be a spot colour, and not a CMYK or RGB process colour) and then drag the slider to the 10% mark (or just fill in the percentage box with "10")