Lighting, Light Fixtures, Ceiling and Exhaust Fans - hard wire

I am installing a vanity mirror with lights and the electricial that come with it has a two prong plug so it can be pluged into a duplex outlet. It has a thumb switch that controls the on/off. I want to by pass the plug and hard wire it so I can use a toggle switch on the wall. When I took it apart I found only black and white wires, no ground. I understand that it is a polarized system. I thought about grounding the supply power to the electic box, but non of the boxes in the rest of the house is grounded this way. In order to work (ground) don't the system have to have all boxes grounded this way.

My question is how can I hard wire this light using a ground wire, or do I need it?

Thanks for your help

yes you can, no, you may not. that being said, you don't need to add a ground. it's just like a table lamp. but you really should not hardwire a fixture like that. perhaps a pro could quote the code to better explain this.