Questions oh wise ones...lick lick
 

1- I am trying to animate a Nurbs jet and moving it around is painfully slow. My hardware is - Athlon XP 2000. GeForce Ti 4600, 128 Mb VGA and 786 Mb of RAM. If I work under wireframe or fast interaction mode then everything is quick. Is my hardware old?
How do you judge the complexity of a model? ie. how do I calculate the poly count...what do I calculate incase of nurbs model???

2-My jet is flying in the sky. I have attached some lights to it but how do I create sun/moon light? DO I put one big light far away on top of the jet?

1. If you go to Display --> Heads up display you'll have several options you can check or uncheck for display, including poly count. Your machine sounds more than able to handle one jet and a couple of lights. Are you using a simple shader or are you viewing the whole thing with large textures (and with hardware-texturing on)? That could be stressing it.

2. You could use a point light with a glow to simulate a sun or moon. Just place it far off in the scene somewhere.