   A Memory Cdc..?
  I am not sure I am going about this the right way, but at any rate, I am creating something along the lines of a paint program and it needs to be able to draw. To do this I use MoveTo and LineTo which are great for drawing on the client. But I also need a copy of these lines on another surface, I cant follow the mouse because there is a tool to draw straight lines and though it draws a straight line the mouse does not actually need to be on the row the line is on. At any rate, I need either to tie a memory dc into a cdc so I can use MoveTo and LineTo, or I need to know how to set the row the mouse is on, without effecting the column, so the mouse would be forced to travel alongside the line and I could just get the points. Thanks,MattI should add I cannot just blt it, as there is a background involved that I do not wish to capture.   
  Are you saying you want to be able to draw lines, that are forced horizontal or vertical only?In that case simply set a variable to the x-coordinate of the starting-point when you start to draw the line, and ignore the mouse x-coordinate later, using only the mouse y-coordinate and the original x-coordinate.   