Freehand Drawing with MCs

I've been trying to get this started for some time now. I've tried a form of API drawing and I've tried a grid of MCs when the mouse is dragged over they change to the brush/colour selected. (This was to resource hungry)

Here's what i want to do... I need the user to be able to draw "freehand" but the MCs have to be a set distance apart. Any thoughts?

I'm using MCs because there will be different frames with different "brushes" in them. If there is an easier way to do any of this let me know.

Cheers, Steve

Can someone point me in the right direction?