Hi Noskule,
MoI has a "perp/perp" snap point that will find that.. Select a tool like the line tool, and click somewhere "near" the apex of the curve or line .. Then move over to the line or curve and slide up and down a bit... At the apex and line tan, a perp/perp snap will appear and the line you are drawing will "jump a bit" to hit that spot...

Hi nos, also see here for an example video:
http://moi3d.com/forum/index.php?webtag=MOI&msg=3042.14

Like Burr says you need to start the first point of the line somewhere in the general area (like within 100 pixels or so) of the perpendicular, and then when you move your mouse over the other curve there will be that "perp/perp" snap available which is the one you want, it's usually just slightly to one side of the single perp snap.

When it kicks in it will read "Perp/Perp" on both sides of the line. That's a special snap that also moves the start point of the line as well.

- Michael

exactly what I was looking for, thanks
nos