What do I need to do to enable desktop sharing on (lubuntu) I want to control it from Ubuntu 11.10, if possible to also do it from a Windows pc would be great. But not if it uses more load or might make the system unstable though.
LXDE/Lubuntu doesn't include any desktop control software, so there is nothing to enable.
You can install stuff like SSH server or VNC, but obviously, whatever you add will use more resources. SSH is probably a lighter option, it's also more secure, but is harder to use. VNC is more user friendly, but isn't secure enough to work over the Internet.
PS: There is also software from the http://www.nomachine.com/.
First, update your installed packages then install
After this you can play remotely. It's awesome.