OK - check out Bridge Builder - it's a little direct 3d program. Basicly you are given a budget and a gap - you design a bridge that fits the budget and then test it with a train too cool. Warning - addictive! http://bridgebuilder.8m.com/download.html
GEE THANKS, another game . Hey I came in under budget on the second try. Bet it gets a lot harder though the farther you go.....Mike