I would have thought that an oracle forum would have got better responses, but here you are.
Oracle uses either of two optimizers, rule based and cost based.
The old rule based was common before Oracle 8, and tries to use the last table mentioned as the driver table.
The cost based Optimizer avilable in oracle 7 on, may prefer the first table to be the driving table but not very strongly.
Using explain plan with either optimizer can show you the choices the optimizer made in your code. you can try to enfluence those choices with hints. I tried to remain child-like, all I acheived was childish.