What I mean is when I try to resize the preview pane, for example.
I need to use a magnifying glass to succeed! :-(
Grrrrrrrr.
If I understand correctly, you shouldn't need to.
When the cursor changes to the double-headed arrow, it is on the border -
just press the button while it is a double-headed arrow, then you can drag.
Don't watch where the mouse is exactly, watch what the arrow looks like.
If you are having trouble moving the cursor slowly enough, you might want
to change your mouse sensitivity/acceleration. You may also find things
like "ClickLock" useful - some mouse drivers have other ways of adjusting
the precision of the movements by holding down keys, etc. If you have a
touchpad instead of a mouse, there are usually additional ways to make it
easier to select the edges of windows, like one that makes the cursor stop
at the edge of a window when you try to move it from inside to outside of
the window.
You could change the width of your window borders, as well.