The pen tool is only in Photoshop, not elements. You can draw freehand with the brush or pencil tools (you can put something on a separate layer below and trace the edge if you need help), or you can draw a selection with the elliptical marquee tool, go to Edit>Stroke (outline) selection to color it, then erase the parts you don't want.
The custom shape tool draws many shapes. It sounds like you have the line tool selected. Hold down its icon in the toolbox and you'll see several other tools in there. The polygon tool with the rounded corners option turned on will draw circles, although it's not supposed to.
If you have a scanner, draw your curved line(s) and scan it.
You could also try using the Shear filter. However, this is not as good as the options Barbara gave you as the line will degrade when it is distorted by the filter.