what is the lightest, smallest laptop mac, that will also allow me to use windows?

11inch MacBook Air.

You can either use Bootcamp (part of OS X) to partition the internal drive and use it as a dual boot machine, or use an applicaton such as Parallels to set up Windows in a virtual environment. The set up you choose depends on you resource requirements.

Based principally on weight, I give the Macbook the edge over the Macbook Air. Look at the specific specifications and decide for yourself.

Ciao.

the Macbook will run an OSX which means that Windows can be installed via Bootcamp.

I do not know what your definition is for a 'proper computer'.

Newbie the Terrible wrote:

Or does keyboard and screen separate into multifunctional purposes?

It is similar to a Macbook Air or Macbook Pro, if the display or the keyboard are separated, one has mangled the computer because they are not designed to be separated.

Ciao.

Apple don't currently make any 'multifunction' type computers.

The MacBook Airs use Intel Core i type processors similar to most laptops.

The 12 inch Macbook uses Intel Core m type processors.

Depending on what you require from a computer will determine which one you would need.