Have you checked your fps? (DXTimer.Framerate) If it's over 100 there wouldn't be much problems.

But you can't achieve fluent drawing using a timer! Either use onMouseMove event or directly handle mouse message using Winapi, both are equally fast and very smooth solutions. Plot lines on those mouse events but flip screen on timer. Or if you don't have animation on your program, then timer is not needed anywhere but you can draw on mouse events...