If you are going to use a Halogen light then you have lots of options. Putting one on a stand outside the window would look pretty harsh and contrasty if it is raw. There is a lot of ambient light mixed in when the sun is shining in the window. The halogen light might look more like moon light.

But if you have a curtain or light translucent cloth or material over the window it will of course soften quite a bit. If you can bring the halogen light in the room you could bounce it off a (hopefully light colored) wall and get very nice broad light quality... sort of like a huge soft box. You will lose a lot of brightness in doing that but it will be brighter than the existing light fixtures. You will still need a tripod... and cable release.