Hi Ditto, there is a sine wave script that you can get from here:
http://moi3d.com/forum/display.php?webtag=MOI&msg=1519.38

That should let you create a basic sine wave and then you can just use regular modeling tools to modify it to your particular needs, like if you need it to start and stop at a particular point just draw in a vertical line at those places that intersects the sine wave curve and use the Edit > Trim command to cut it.

- Michael