It smooths fine on my Windows system in GL when the mouse button is down, and it's sharp/jaggy with it up.
I then commented out "SetGraphicsDriver GLMax2DDriver()" to test DX and got "DebugLog:AA not supported" when pressing the mouse button (and the line remained sharp/jaggy). That was with my ATI Catalyst video driver at its default AA of "Use application settings." Turning it on manually in the control center provided AA smoothing for the line regardless of whether the mouse button was pressed or not (no DebugLog error when pressing it).
Your 9800 Pro might do the same?
I then commented out "SetGraphicsDriver GLMax2DDriver()" to test DX and got "DebugLog:AA not supported" when pressing the mouse button (and the line remained sharp/jaggy). That was with my ATI Catalyst video driver at its default AA of "Use application settings." Turning it on manually in the control center provided AA smoothing for the line regardless of whether the mouse button was pressed or not (no DebugLog error when pressing it).
Your 9800 Pro might do the same?