First you laptop must not disable the wireless when you plug in the ethernet cable. This is a bios setting in some.
It can be done but it requires you to tell the PC EXACTLY what "browse the internet" and "download" really mean to you.
It is all done with the ROUTE command. The key thing is you need to remove the default gateway on one of the 2 interfaces and then manually add route statements to send traffic to that interface...leaving the rest to use the default statement on the other interface.