snapping to intersection point btwn target edge/face and line of translation?

Suppose I want to move vertex A to the red dot on edge BC:

http://i456.photobucket.com/albums/qq284/pellaamarilla/visualaid1.png

Locking translation to the Y axis, and with snap to edge on, the destination point depends on where on the target edge I point:

http://i456.photobucket.com/albums/qq284/pellaamarilla/visualaid2.png

So how do I do this? Can I lock the snapping target to a particular axis somehow?

thx for compliment my gimp artworks i work on then long hours

Basically, as in your image, extrude the vertex in Y direction of a given distance. In pic A, I extruded 16.8 there with Edge Length turned “on”. In pic B, I used that extruded vertex as a point to “snap”, to knife cut vertical; [K] for knife hot key, [Ctrl] + LMS the vertex, drag the cut line up than MMS snap to vertical, LMS to end cut layout process, then [Enter]. That’s the way I do it with Blender 2.49.

http://i1135.photobucket.com/albums/m626/cabby24/Blender%20Pics%202011/cut_tosize.png

Man I still cant snap in 2.57!

Ah I see. So it will always be a multi-step process. It could be more intuitive imo, but maybe then I should learn python and make it so. Thx!

Edit:

…yeah, I just discovered that I can’t snap with the knife tool in 2.57 either. This puts my work at a standstill…

You can use the Edge Tools addon after you have extruded vertex A to create an edge http://wiki.blender.org/index.php/Extensions:2.5/Py/Scripts/Modeling/Edge_Slice

Demo http://screencast.com/t/ezFGwKW1oN

Perfect! Much obliged.