I'm not sure how well vino-server integrates into the LXDE desktop - were you able to find the vino-preferences setup application in order to actually start the server? if not, try invoking it from a terminal
You can also check that it's running using ps or pgrep
If all checks out OK then the next step would be to check the listening port
ps -ef | grep [v]ino-server
(run on the server)
sudo netstat -nlp | grep vino
Are you tunneling the connection over SSH or using plain VNC? are the Windows laptop and the Lubuntu laptop on the same LAN?