The only 18" (18.4" to be precise) laptops I've come across recently that more or less meet your required specs & often surpass them are the:
- Acer's 8920G range click here
- Sony's AW11 range click here
- HP's new HDX range click here (due out in a week or so).
Have a look on each manufacturers' website for more details, & possibly more models as well. Shop around as the above links may not be the cheapest. G