Dell even sell Laptop MotherBoards?

Your best bet is to trying finding one on Ebay.

Does anyone know if an Inspiron 5100 will only work with it's own power supply cord. I have tried different models and different adapters, none of them worked. So I am not positive.

I was able to use an similar model on an old laptop I had, so I would have to say if the connector fit and the wattage was the same, you should be fine.

Has anyone else seen the New Dell XPS Laptop.

Yes, it is very nice, a little bit cheaper than the Alienware, but the Alienware is smaller, better looking, lighter, and has a swappable video card.