Beavis,
There are no external Video cards for Notebooks that I am aware of. The only thing that I have seen is a type of Video capture card or something of that.
The only systems that we know that will work are the ones that we sell on our Site,
http://www.mtu.com/basics/karaoke-laptop-2.htm
You might beable to get a High-End Dell model that would work, such as the Dell Inspiron 8600, 9100 or XPS.
If choosing any of these Dell Laptops, I would recommend only getting the ATI Radeon Graphics chip in them over the NVIDIA, you will have less problems in the future.