Holding 'X' key after selecting the verts and using move tool will snap them to the default grid, making them planar in the ortho you are using...if thats what you meant. Also works if you want to snap them to a vert as the base point. Select the verts you want to align to a base vert...then 'V' and use the move tool arrow indicators to do this....

cheers bullet

I forgot to add..turn off 'Retain Component Spacing' in the tool options box for the above to work.