Normally I would say use the networking to share files between computers, however XP & windows 7 do not speak the same languge (silly).
As far as I am aware, google sorts the files only on the computer they are actuually stored on.
You might be better off (in Picassa) exporting the photo's you want to a memory stick and plug that into the laptop and Visa-versa..
On Picassa, if you Export, you get a clean copy of the latest adjustments.
Hope this helps