I have already written about simulating the laptop's display with
Xephyr, with color swizzling, antialiasing, and a postprocessing to
restore good luminosity.
There is a last process that is useful in previewing what things will
look like: "shrinking" reduces the size of images by half in a way
that takes the color swizzling into account (see  for more details
on all these processes). Half-sized images are a good preview of the
overall feeling of the laptop's display, since they should
approximately have the right dimension (considering that the
resolution of common screens -- 96 dpi -- is half that of the OLPC
display -- 200 dpi).
Using these simulation tools, I've written a small review of several
theme and graphical elements (fonts, thin lines, buttons, etc.) here: