the pen tool is used for creating splice paths, which are an aid for selection and masking and stroking, but it is not a tool for directly drawing lines. the pen tool is poorly named & should really be called the path tool. you can use the brush tool or the line tool to draw lines. you can use the "pen" to create paths that may be selected and stroked with the currently selected brush. (caveat: i'm still using photoshop v5, so the preceding description may be totally obsolete!)