Moving point along plane

Hi,

Given a point p (having a direction n), I want to move it perpendicular to n until p'+dn = (0,0,0). What the best way to calculate the distance d?

I thought this would be quite simple, but unfortunately I'm feeling quite simple today.

Thanks for any help.

Ok, it is pretty simple, just having a slow day.
First n is rotated to be (0,1,0) {could have been parallel to any axes} using rotation matrix A.
Point p is then rotated around (0,0,0) using the same matrix to become p'.
The x & z components of p' are set to zero to become p", which now lies on the y axis. The distance to p" is simply the y component of p' (or p").