How do i set the RAWMOUSE structure to give me the relative Position of the mouse cordinate at the lLastX and lLastY instead of absolute position? or vice versa?

First off, you need to find the center of your window, setting the cursor's position to the center of the window (using SetCursorPos()), and then, on any mouse movement messages, find the position of the cursor (using GetCursorPos()), calculate the difference (which'll give you what you want), and if it's moved, recenter the cursor. You'll need to update the center of the window when it's moved/resized, but it's a fairly simple way to get the job done.

You could keep a copy of the last X,Y values and when you want to get a relative position then you can get the difference between the current set and the old set.