pathfinding help!

Pathfinding in a real city isn't necessarily any different from doing it in a game. A* and Dijkstra both work well in their respective ways. What will work best for you depends on your exact need.

There's some reasonable information on ant colony optimisation on Wikipedia, including links to references. Is that sufficient?

I recommend IDA* algorithm for games. It's a variant of A* which searchs in depth-first mannar. It's a bit complex than A* but has some nice features.

You can find details here:
http://www.gamasutra.com/features/20000626/brockington_01.htm

well, i try to implement A* now. but how can i handle one way road or street ?
any idea?

A* has a part where it generates successor nodes for the current node being examined. When you generate these nodes to explore in the future, don't generate them for areas where you would need to pass down a one way street to get there.